Next Article in Journal
Phytochemical and Antioxidant Variability in Some Black Mulberry, Chokeberry, and Elderberry Cultivars in Relation to Cultivar, Plant Part, and Extraction Solvent
Previous Article in Journal
Evolutionary Forces Shaping Trans-Species Polymorphisms in Genus Cucumis
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Horticulturae
Volume 11
Issue 5
10.3390/horticulturae11050453
horticulturae-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Reproductive and Pollination Characteristics of Three Understory Impatiens Species

by
Yuxi Xue
1,2,
Qitao Su
2,*,
Yuxin Zhang
2,
Shujian Zhang
2,
Heng Li
2,
Leiqin Liao
2,
Jia Zeng
2,
Weiyuan Huang
2 and
Yian Xiao
2,*
1
College of Tropical Agriculture and Forestry, Hainan University, Haikou 570228, China
2
Key Laboratory of Jiangxi Province for Biological Invasion and Biosecurity, School of Life Sciences, Jingangshan University, Ji’an 343009, China
*
Authors to whom correspondence should be addressed.
Horticulturae 2025, 11(5), 453; https://doi.org/10.3390/horticulturae11050453
Submission received: 26 March 2025 / Revised: 21 April 2025 / Accepted: 22 April 2025 / Published: 23 April 2025
(This article belongs to the Special Issue Advanced Studies in Cultivation and Breeding Propagation of Ornamental and Aromatic Plants and Their Use in Landscaping Design)
Browse Figures
Versions Notes

Abstract

:
Understory flowering plants often face limitations in pollinator availability. This necessitates an investigation of pollination mechanisms and reproductive traits to understand their survival strategies. Floral syndromes, which are critical determinants of plant–pollinator coevolution, significantly impact the reproductive success and diversification dynamics of angiosperms. The genus Impatiens is known for its remarkable floral diversity and varied pollination systems and it is also serves as an exemplary model for examining plant–pollinator interactions. Therefore, this study was performed to elucidate the pollination characteristics and breeding systems of three sympatric species, Impatiens davidii, Impatiens jinggangensis, and Impatiens commelinoides. The results indicated all the Impatiens species exhibited similar individual flower longevity (4–5 days). However, I. commelinoides and I. jinggangensis peaked in July-August, whereas I. davidii primarily flowered in August-September. These species shared a self-compatible breeding system that requires pollinators for facultative outcrossing, with bumblebees (Bombus) and polyester bees (Amegilla) identified as the primary pollinators. The presence of wing petals had a significant impact on fruit set in both I. davidii and I. commelinoides. The three Impatiens species demonstrated notable interspecific differences in their floral scent profiles, accompanied by distinct variations in floral morphology and scent characteristics. These differences collectively represent pollination strategies and life-history tactics that highlight pronounced interspecific divergence. The variation in pollination strategies is attributed to the synergistic interaction between floral morphology and scent chemistry. Thus, these findings offer valuable insights for the investigation of forest understory plant conservation, resource utilization, and co-evolutionary relationships with primary pollinators.

1. Introduction

Understory plants are an integral component of the forest ecosystem, and they have remarkable species diversity and ecological adaptability [1]. These plants also play a vital role in soil water retention, water conservation, and windbreak/sand fixation, and they are also a primary foundation of forest biodiversity and sustainable ecosystem development [1,2]. The presence of understory plants increases the floristic diversity [3,4] ecosystem functionality [5] and facilitates nutrient cycling and biomass accumulation [6]. Therefore, investigating the reproductive traits and pollination characteristics of understory plants is essential, as these intrinsic drivers critically shape the species composition and dynamic changes in understory plant communities. The dynamic plant–pollinator interactions represent key drivers of floral evolution. Within shared habitats, pollinator-mediated selection promotes floral trait convergence among sympatric species [7,8]. However, topographical and elevational gradients induce intraspecific variations in pollination strategies, manifesting as differential pollinator assemblages, visitation frequencies, and behavioral patterns [9,10]. These geographical and environmental heterogeneities drive repeat transformations in pollination systems, accompanied by corresponding floral trait modifications [11].
Floral architecture and breeding systems critically determine reproductive success through their ecological constraints and hold significant implications for biodiversity conservation and interspecific coordination [12]. The strategic spatial–temporal separation of pistils/stamens and sequential flower maturation enhance interplant genetic exchange [13], thereby improving offspring fitness. Angiosperms rely on external vectors for pollen transfer, employing nectar or pollen to modulate pollinator visitation patterns [14]. These floral rewards optimize pollinator fidelity, promote outcrossing efficiency, and mitigate inbreeding depression, which are essential mechanisms for population sustainability [14,15].
Pollination syndromes reflect co-evolved trait matching between flowers and their pollinators. This typically involves multidimensional adaptations in floral dimensions, coloration, morphology, and scent profiles [16,17]. Notably, certain floral traits exhibit synergistic effects on pollinator attraction, where isolated traits show limited functional significance [18]. The floral spur, a nectar-producing structure connected to the labellum in Impatiens species, exemplifies such adaptive specialization. Its dimensional characteristics (length, shape, coloration) directly influence both pollinator selection (via proboscis length matching) and nectar-production dynamics [19,20,21]. Comparative studies on sympatric Impatiens species reveal spur length as the primary determinant of pollination syndrome differentiation [22]. Evolutionarily labile pollination systems undergo functional shifts across geographical and environmental gradients, accelerating adaptive radiation and speciation events [23,24,25]. Pollinator-mediated selection remains the principal driver of angiosperm diversification and floral trait evolution [26].
The genus Impatiens, comprising over 1000 species globally, represents a characteristic understory herbaceous taxon. Its floral structures exhibit remarkable morphological sophistication and chromatic diversity, demonstrating specialized adaptations to pollinators and earning the designation “dicotyledonous orchids” [27]. China serves as a major distribution center for this genus, with approximately 352 documented species [28]. Continuous botanical exploration has led to the discovery of numerous novel species [29,30,31], particularly given the genus’ pronounced regional endemism and strict habitat specificity, making it an exemplary system for studying plant–pollinator interactions in understory ecosystems [17]. Two primary pollination syndromes including bombus-pollination syndrome and bird syndrome dominate in Impatiens [32]. Impatiens species mainly use Bombus and Macroglossine as pollinators in China [33,34,35,36,37,38,39]. In contrast, African Impatiens species show both chiropterophilous and myophilous adaptations [40], while I. rivularis in Madagascar is exclusively myophilous [41]. Nevertheless, a comprehensive understanding of their reproductive strategies remains incomplete. The volatile compounds generally serve dual functions: pollinator selection through species-specific attraction and the exclusion of non-target visitors, and the chemical composition of floral emissions is adaptive to dominant pollinators’ olfactory preferences [42]. Concurrently, floral morphology (including shape and coloration) exhibits parallel adaptive specialization to primary pollinators while functioning as a mechanical filter against secondary visitors [43].
Pollination syndromes in plant species are often described based on floral morphological traits. However, comprehensive studies integrating both floral scent and morphological traits remain scarce. This study combines the flowering phenology, floral morphological characteristics, and floral scent profiles of understory plants to investigate pollination strategies in Impatiens species. Specifically, it also analyzed how the floral scent, morphology, and pollination ecology collectively shape divergent pollination strategies. Therefore, three endemic Chinese Impatiens species (I. davidii, I. commelinoides and I. jinggangensis) were selected, which are restricted to narrow habitats in Jiangxi and Hunan provinces. Despite their overlapping altitudinal distributions and significant flowering period overlap in Jinggangshan Mountain, most Impatiens species exhibit habitat specificity, yet the drivers of their speciation remain unclear. Pollinators have been proposed as a potential factor in their differentiation; this explanation remains partial. Therefore, this study aims to (1) analyze differences in phenological traits, plant traits, and floral structures among the three understory Impatiens species and assess their impacts on reproductive success; (2) to characterize their breeding systems and pollination mechanisms.

2. Materials and Methods

2.1. Study Area

This study was conducted in the Jinggangshan Mountain region of Jiangxi Province, situated in the central Luoxiao Mountain range, southeastern China. The area exhibits a subtropical monsoon climate characterized by distinct seasonal variations and high humidity, with a mean annual temperature of 14.2 °C. Monthly temperatures range from 3.2 °C in the coldest month to 23.9 °C in July (peak summer), reaching extreme highs of 34.8 °C [44]. The study site has an annual precipitation of 1856.3 mm distributed across 213 rainy days, ensuring consistent water availability. The region receives 1511 annual sunshine hours with 96 fog days annually, reflecting a unique ecoclimate integrating elevated humidity and moderate solar radiation.
Three Impatiens species co-occur with characteristic understory companions, including the following: Rubus, Mallotus, Boehmeria, Cnidium, Hypolepis, Gonostegia, and Oenanthe (Table 1). To control for the altitudinal effects on pollinator assemblages, we selected study plots within comparable elevation ranges. The population selection criteria required a minimum stand area >2 m2 with more than 30 reproductive individuals per population.

2.2. Methodology

2.2.1. Flowering Phenology and Morphometric Measurements

Flowering phenology was monitored through daily observations of 10 randomly tagged flower buds from distinct individuals until anthesis. Post-anthesis, floral developmental stages were recorded twice daily (09:00 and 16:00). The floral longevity was quantified as the duration between full corolla expansion and terminal wilting. The community flowering period encompassed the interval from the initial bloom to final floral senescence within experimental plots. Sexual phase durations were categorized as follows: (1) Pistillate phase, stamen abscission to complete floral senescence; (2) staminate phase, initiation of anther dehiscence to stamen detachment. Morphometric analyses were conducted on 30 randomly selected flowers and 30 individual plants. Floral traits (corolla dimensions, nectar guide patterns) and vegetative traits (plant height, basal stem diameter, leaf length/width) were measured using digital vernier calipers (0.01 mm precision).

2.2.2. Pollen Viability and Nectar Sugar Concentration

In three study plots, thirty flower buds from distinct individuals were randomly sampled, isolated, and labeled using a bagging treatment to prevent pollinator interference. Three flowers were subjected to staining treatment on days 1, 2, and 3 of floral anthesis, respectively. Samples were incubated in 1.5 mL centrifuge tubes containing TTC, protected from light, and transported to the laboratory. Three 10 μL aliquots per tube were transferred to slides, covered with coverslips, and incubated at 25 °C for 30 min. Pollen viability was quantified microscopically (BK 6000) using standardized criteria: fully stained (1), partially stained (0.5), or unstained (0) grains [12].
For the nectar analysis, 10 bagged flowers from distinct plants were sampled at anthesis. The nectar volume was measured using glass capillaries (0.11 mm inner diameter × 75 mm length) inserted to the nectar spur base, calculated as V = πr2h. The sugar concentration was determined with a handheld refractometer.

2.2.3. Pollen–Ovule Ratio and Out-Crossing Index (OCI)

Ten unopened flower buds were randomly collected from the three study plots and preserved in a portable icebox at 4 °C. These samples were transported to the laboratory within 2 h for processing. Using precision needles and forceps, the floral structures were dissected to isolate anthers and stigmas, which were immediately transferred to 1.5 mL centrifuge tubes containing a 75% ethanol solution [34]. The anthers were mechanically disrupted with dissection needles to create a homogeneous pollen suspension, which was then diluted to a final volume of 1 mL. A 10 μL micropipette was used to aliquot 5 μL of the suspension onto glass slides, with three replicates per sample. Pollen grains were quantified under a KB 6000 bright-field microscope, and the total pollen grains count per flower was calculated by multiplying the observed values with the dilution factor. Simultaneously, stigmas were separated using stereomicroscopy-guided dissection needles to count the ovules per flower. Based on these floral trait measurements, the outcrossing index (OCI) for the three Impatiens species was calculated following Zhong’s methodology [34].

2.2.4. Breeding System Analysis

To investigate the breeding systems of three Impatiens species, five experimental treatments were implemented for each taxon following standardized reproductive biology protocols: autonomous autogamy, control group, agamospermy, geitonogamy, and xenogamy. For each treatment, 30 flower buds were randomly selected and labeled. The control group received no manipulation. In autonomous autogamy, a bagging treatment was applied one day before anthesis to exclude pollinator interference with the plant’s capacity for spontaneous self-pollination. In agamospermy, stamens were removed followed by bagging to assess asexual seed formation. Geitonogamy means the transfer of the pollen from a flower to the stigma of another flower of the same individual. In xenogamy, pollen from the mature stamens of a different population (at least 10 m apart) was applied to the target stigma.

2.2.5. Observation of Pollination Characteristics and Effects of Floral Components on Seed Setting

A square observation quadrat with a side length of 1 m was established in the Impatiens community, and the number of flowers in the quadrat was recorded. The species, pollination sites, and pollination behavior of flower-visiting insects were recorded during the observation, and the flower-visiting frequency was calculated. Pollination was observed from 7:00 a.m. to 6:00 p.m. After observation, the flower-visiting insects were captured using insect nets, poisoned with poison bottles, and brought back to the laboratory to make specimens to identify the species.
To investigate the impact of floral components on fruit set rates in three Impatiens species, five experimental treatments were systematically implemented within each study plot: removing flower spacing, removing lips, removing wings, removing flags, and natural control group.

2.2.6. Floral Volatile Collection

Volatile organic compounds from Impatiens species were collected using solid-phase microextraction (SPME) methodology. The standardized protocol entailed the following: (1) harvesting freshly opened flowers under clear sky conditions from five distinct individuals randomly selected across three study plots; (2) enclosing five fully expanded flowers per plant in a single headspace vial; (3) labeling specimens and maintaining a chain of custody through ice-chilled transportation to the analytical laboratory. Four biological replicates were established for each Impatiens species within the same study plot.
Volatile compounds were analyzed via gas chromatography-mass spectrometry (GC-MS) under optimized parameters. The operating conditions for gas chromatography were as follows: the inlet temperature was set to 250 °C, and the initial column temperature was 30 °C. The temperature program consisted of four stages: (1) in the first stage, the temperature was increased to 50 °C at a rate of 10 °C/min and held for 3 min; (2) in the second stage, it was increased to 100 °C at a rate of 2 °C/min; (3) in the third stage, the temperature was increased to 140 °C at a rate of 1 °C/min; and (4) in the fourth stage, it was increased to 280 °C at a rate of 15 °C/min. The system pressure was maintained at 45.8 kPa. Helium with a purity of 99.99% was used as the carrier gas, with a flow rate of 1 mL/min in splitless mode. For mass spectrometry, the ion source temperature was set to 290 °C, the injection port temperature was set to 250 °C, the scanning mass range was 30–450 amu, and the electron multiplier voltage was set to 1.22 kV. Compounds were identified through NIST library matching (match factor >85%) and quantified via peak area normalization. Only compounds detected in ≥3 biological replicates were retained for the subsequent analysis.

2.2.7. Data Analysis

The experimental data were processed using micro-soft Excel 2019, and R 4.4.1 software was used for data analysis and drawing. A T-analysis was used to analyze the differences in floral traits. We used reduced-order analysis (PCA) to analyze the pollination characteristics of three the Impatiens. The relationship between the pollination characteristics of the three Impatiens was comprehensively analyzed based on the pollination frequency of the main pollinators, the number of cones in the pod, aromatic alcohols, terpenoids, aromatics, the flower spacing length, and the pollinator tongue length. A similarity analysis (ANOSIM) was performed using the R vegan ver. 2.6.8 package [45] to corroborate the floral scent variation patterns detected via principal component analysis. Data visualization was performed using ggplot2 (version 3.3.3) within the R statistical computing environment [46].

3. Results

3.1. Analysis of Flowering Phenology, Plant Traits, and Floral Traits in Three Species of Impatiens

The single flowering period of I. davidii was the longest. The flowering period of the three species of Impatiens overlaps from August to September (full-bloom flowering period, Table 2), and the fruit period of the three species of I. jinggangensis generally ends in November. The pistil flowering period of the three Impatiens species was shorter for 1–2, and the stamen flowering period was longer for more than 3 day (Table 2).
All three Impatiens species shared three key characteristics: (1) zygomorphic annual herbs with axillary pedicels bearing hermaphroditic flowers; (2) corolla comprising a banner petal, bilobed wing petals (basal and upper lobes), funnel-shaped labellum with dorsally recurved spur, and paired lateral sepals; (3) specialized basal wing lobes providing insect-landing platforms.
The one-way analysis of variance revealed significant interspecific spur length variation. I. jinggangensis possessed the longest spur (25.03 ± 6.00 mm; Table 3), whereas I. davidii exhibited the shortest spur (6.13 ± 1.05 mm; Table 3) with unique dual parallel spurs. The labellar spur morphology showed progressive structural differentiation across species gradients. The K-means clustering of morphological traits further separated I. jinggangensis and I. commelinoides into one morphogroup, while I. davidi formed a distinct cluster (Figure 1).
Among the three Impatiens species studied, I. jinggangensis exhibited the tallest plant height (Table 4). The significant differences were also observed in the leaf morphology among the three species. The leaves of I. jinggangensis tended to be narrow and elongated, accompanied by thicker basal stems, resulting in a distinct plant architecture compared to the other two species. In contrast, I. commelinoides displayed a notably shorter stature, with its basal stem diameter being significantly smaller than that of the other two species.

3.2. Pollen Viability, Nectar Volume, and Nectar Sugar Concentration

The sugar content of I. jinggangensis species was significantly higher than that of the other two Impatiens species (Figure 2C). There was no significant difference in the sugar content of the nectar of the three Impatiens, and the sugar content of the nectar of I. davidii was the highest (Figure 2C). Significant differences in the sugar volume were observed among the three Impatiens species. I. commelinoides exhibited a significantly greater nectar volume compared to the other two species, while no statistically significant difference was detected between I. davidi and I. jinggangensis (Figure 2D).
The pollen activity of I. davidii (Figure 2E) and I. commelinoides (Figure 2G) was higher on the first day, and it showed a constant decrease over the time. The pollen activity of I. jinggangensis was the highest on the second day, and overall, it was first increased and then decreased (Figure 2F).

3.3. Pollen–Ovule Ratio (P/O) and Out-Crossing Index (OCI)

The outcrossing index (OCI) values of the three Impatiens species from Jinggangshan were calculated following standard hybridization criteria. All three taxa demonstrated an OCI = 4, indicating partial self-compatibility with predominant xenogamous reproduction requiring pollinator mediation for effective cross-fertilization. Furthermore, the three studied Impatiens species exhibited pollen-to-ovule (P/O) ratios exceeding 2108 (Table 5), confirming their status as obligate outcrossers. Sometimes, The three Impatiens species also exhibited significant differences in pollen count, ovule count, and pollen-ovule (P/O) ratio (Table 5). Controlled pollination experiments revealed that I. davidii, I. commelinoides, and I. jinggangensis maintained self-compatibility while exhibiting predominant outcrossing strategies. This suggests that these species employ a mixed mating system evolutionarily optimized for xenogamous predominance with retained selfing capacity under pollinator-limited conditions.

3.4. Breeding System and Floral Trait Effects on Fruit Set

The results indicate that I. davidii demonstrated neither apomixis nor autonomous autogamy, with natural control groups exhibited significantly higher fruit set rates compared to self-pollination treatments. Autonomous autogamy was observed exclusively in I. jinggangensis, while I. davidii and I. commelinoides showed no evidence of autonomous self-pollination. Under experimental conditions, Impatiens commelinoides displayed no significant differences in fruit set rates among self-pollination, outcrossing, and natural control treatments. Under natural pollination regimes, the fruit set hierarchy was I. jinggangensis > I. davidii > I. commelinoides.
Notably, a quantification of the fruit set under natural conditions (devoid of artificial manipulation) across three Impatiens species was performed (Figure 3A–C). I. commelinoides exhibited significantly lower natural fruit production (5.82 ± 0.97) compared to the other two species, whereas I. jinggangensis achieved significantly higher natural fruit set rates (9.31 ± 0.38). The reduced natural fruit set in I. commelinoides may correlate with its limited pollen availability.
I. commelinoides and I. jinggangensis showed comparable seed sets between natural pollination and outcrossing treatments, whereas I. davidii exhibited significantly higher natural seed sets. No autonomous apomixis occurred in any species. Both I. davidii and I. commelinoides lacked spontaneous autogamy, with manual self-pollination producing an equivalent seed set to cross-pollination. In contrast, I. jinggangensis demonstrated functional autogamy (Figure 3), though its autonomous selfing rate remained statistically indistinguishable from the outcrossing success.
Wing petal removal significantly reduced the seed set in I. davidii and I. commelinoides compared to other floral manipulations but not in I. jinggangensis. No significant differences emerged between other experimental treatments and natural controls, though all manipulated groups showed a numerically lower seed set with greater variability. The non-significant trends suggest the potential compensatory roles of residual floral structures in reproductive success. Notably, spur removal showed no significant impact on the seed set, indicating that this structure may not serve as a primary pollinator attractant in these species.

3.5. Pollinator Observations and Foraging Behavior

I. davidii attracted three floral visitors: Bombus trifasciatus, Macroglossum sp.1, Argalictus resurgens, and B. trifasciatus accessed nectar through the floral tube by landing on wing petals and extending its proboscis into the spur, resulting in pollen deposition on its dorsal thorax. A. resurgens exclusively foraged on staminate flowers for pollen consumption, thus excluding them as legitimate pollinators. A comparative analysis revealed significantly higher visitation frequency by B. trifasciatus (0.796 visits per flower per hour, Figure 4A), establishing its role as the primary pollinator.
I. jinggangensis hosted five visitor species: Amegilla mesopyrrha, B. trifasciatus, Apis cerana, Macroglossum sp.1, and A. resurgens. Nectar-foraging B. trifasciatus and A. mesopyrrha exhibited identical pollen-transfer mechanisms through spur probing. In contrast, pollen-feeding A. cerana and A. resurgens showed an exclusive preference for staminate flowers. Visitation rates demonstrated A. mesopyrrha as the dominant pollinator (Figure 4B). Although A. cerana exhibited the highest visitation frequency among floral visitors, empirical observations revealed that its foraging activity was almost exclusively restricted to staminate-phase flowers, with negligible interactions with pistillate-phase flowers. Given that effective pollen transfer constitutes the defining criterion for pollinator classification, A. cerana was not designated as a primary pollinator in this experimental framework.
The floral visitors of I. commelinoides include Amegilla pseudobomboides, Macroglossum sp.1, A. resurgens, and an unidentified species of Amegilla sp.1. Similar to A. cerana, A. resurgens primarily visits staminate-phase flowers and rarely forages on pistillate-phase blossoms. Consequently, A. resurgens was not classified as a primary pollinator in this study. Among these, A. pseudobomboides was identified as the primary pollinator. During nectar foraging, these bees land on the wing petals, enter the floral tube, and extend their proboscis into the nectar spur to access nectar, with pollen adhering to their dorsum during this process. In contrast, the smaller-bodied Amegilla sp.1 exhibited nectar-robbing behavior by directly accessing the nectar spur without contacting the reproductive structures. Results demonstrate that the visitation frequency of A. pseudobomboides (0.15 visits per flower per hour) is significantly higher than that of the other two insect groups (Figure 4C). Furthermore, A. pseudobomboides primarily visited I. commelinoides during morning and afternoon periods, while elevated temperatures suppress its activity [47], thereby influencing the visitation frequency.
Significant divergence emerged in spur lengths and pollinator proboscis dimensions among three Impatiens species (Table 3). All species exhibited stigma access corridors (width/height: 29.04 ± 3.47 mm in I. davidii, 30.27 ± 4.24 mm in I. jinggangensis, 34.57 ± 4.17 mm in I. commelinoides) sufficiently spacious for pollinator entry. These dimensions significantly exceeded pollinator body constraints, enabling nectar acquisition through the floral tube while ensuring dorsal pollen loading during visitation.

3.6. Composition of and Variation in Floral Volatile Organic Compounds (VOCs) in Three Impatiens Species

The floral scents of the three Impatiens species were primarily composed of fatty acid derivatives, terpenoids, and aromatic compounds (Table S1). A total of 20 fatty acid derivatives, 6 terpenoids, and 3 aromatic compounds were identified. I. davidii exhibited two dominant constituents: ethyne, fluoro- and linalool. I. jinggangensis predominantly contained ethylhydrogenoxalate and styrene. In contrast, I. commelinoides displayed a more dispersed scent profile, with the major constituents including styrene, 1-octen-3-ol, 3-octanone, 3-octanol, and ethyne, fluoro-, the latter showing the highest concentration among them.
Principal component analysis (PCA) was performed on the floral scents of the three Impatiens species (Figure 5A). The first two principal components collectively explained 66.6% of total variance, PCA axis 1 explained 37.5% of the total variation in the data, while PCA axis 2 explained 27% of the total variation in the data. The PCA plot revealed distinct clustering patterns, with no overlap between I. davidii and the other two species. Non-parametric Kruskal–Wallis tests on the two principal components showed significant differences in floral scent profiles between the species (PC1: χ2 = 9.8462, p = 0.007277; PC2: χ2 = 8, p = 0.01832), indicating that PC1 and PC2 effectively distinguished the floral scents of the three species. These findings suggest significant interspecific variation in the chemical composition of floral scents. Notably, terpenoids were significantly more abundant in I. davidii compared to the other two species. Fatty acid derivatives did not differ significantly between I. davidii and I. commelinoides but were significantly lower in I. jinggangensis. No significant differences were observed in aromatic compounds.
Additionally, ANOSIM analysis (Figure 5B) corroborated the PCA results, revealing a high degree of dissimilarity between the floral scents of the three species (R = 0.9583, p = 0.001). Both analyses collectively demonstrate significant differences in the floral scent profiles of the three Impatiens species.

3.7. Floral Trait Differentiation Among Three Impatiens Pollination Strategies

The principal component analysis (PCA) of floral scent profiles and morphological traits revealed significant divergence across the three pollination strategies (Figure 6). The first two PCAs collectively explained 70.7% of total variance with PCA axis 1 explained 43.7% of the total variation in the data, while PCA 2 explained 27% of the total variation in the data. I. jinggangensis and I. commelinoides exhibited scent profiles dominated by aliphatic derivatives (62.3% relative abundance) and aromatic compounds, coupled with elongated floral spurs matching their primary pollinators’ proboscis lengths. In contrast, I. davidii displayed the shortest spurs (Table 3) but highest terpenoid content, correlating with the elevated visitation frequency by its specialized pollinators. Notably, the PCA revealed a significant negative correlation between spur length and pollinator visitation frequency (Figure 6). A positive correlation existed between the spur length and pollinator proboscis dimensions: species with elongated spurs primarily attracted long-tongued pollinators, whereas short-spurred counterparts interacted with short-tongued species (Figure 6). This structural match suggests specialized nectar-access strategies while maintaining effective pollen-transfer mechanics.

4. Discussion

Impatiens species typically inhabit understory and forest edge environments, representing classic understory herbaceous plants. Their pollination process relies on specialized pollinator communities that demonstrate unique adaptive functions in complex habitats characterized by low light intensity and high humidity. Compared to open habitats, understory pollinators have evolved light-sensitive visual systems, efficient antennal olfactory localization capabilities, and flexible flight patterns adapted to dense vegetation [48]. The pollinator visitation frequency, pollen load, and specificity directly influence pollination efficiency in these plants [49]. Impatiens species exhibit generalized pollination systems that have undergone multiple evolutionary shifts [17]. The studies suggest that secondary pollinators may represent vestiges of ancestral pollination systems [50]. Consequently, these secondary pollinators constitute functional redundancy in Impatiens species, and their redundancy–complementarity dynamics further enhance the stability of the pollination ecology. Additionally, morphological coevolution between pollinators and plants improves pollination precision and reduces pollen waste [7], which aligns with our experimental findings.
The flowering phenology of Impatiens plants serves as the foundation for understanding plant pollination, breeding systems, and reproductive success, and it also constitutes a significant research domain in reproductive biology [51]. The peak flowering periods of I. jinggangensis and I. commelinoides primarily occur from July to August, while that of I. davidii spans September to October (Table 2). During this period, the Jinggangshan Mountain area exhibited suitable temperatures and reduced precipitation, conditions favorable for the activity of their primary pollinators, Bombus spp. Although the individual flower longevity of these three Impatiens species was relatively brief (4–5 days), with pistil receptivity lasting only 1–2 days, this trait aligns with the flowering characteristics observed in other understory species [52,53]. The prolonged collective flowering duration facilitates successful community reproduction. Concurrently, the temporal overlap in flowering phases enhances the pollinator visitation frequency and diversity [54]. The sequential exposure of pistils and stamens across developmental stages in these three Impatiens species effectively prevents autogamy. Furthermore, the staggered maturation of male and female reproductive organs within individual flowers inhibits intra-plant pollination, thereby enhancing inter-plant genetic exchange, mitigating the risks of inbreeding depression and ensuring adaptive fitness in progeny populations [55].
Plant functional traits manifest through resource-utilization strategies and reproductive characteristics, reflecting adaptive mechanisms that influence growth, reproduction, and survival [56]. Floral traits are intrinsically linked to reproductive functional adaptations [57]. Ovule-to-pollen ratios and bagging experiments across the three Impatiens species indicate a facultative outcrossing breeding system characterized by self-compatibility and pollinator dependency, consistent with prior studies on Impatiens reproductive biology [13]. Notably, autonomous autogamy occurred in bagged treatments of I. jinggangensis, potentially attributable to the inherent pollen characteristics of Impatiens. Under pollinator exclusion, this self-pollination mechanism represents an adaptive reproductive strategy to ensure population persistence under pollination limitation [58].
The results revealed that I. commelinoides exhibited significant differences in fruit set rates between natural controls and autonomous self-pollination treatments (Figure 3F). Significant disparities were also observed between outcrossing and natural fruit set rates, as well as between outcrossing and selfing fruit set rates. The breeding system of I. davidii predominantly relies on outcrossing, demonstrating self-compatibility without apomixis or autonomous autogamy. Consequently, its reproductive success largely depends on pollinator-mediated pollination. The outcrossing breeding system not only enhances population genetic diversity but also improves the adaptive capacity under ecological fluctuations [52]. This is a strategy of significant ecological importance for Impatiens species facing complex environmental pressures. In I. jinggangensis, natural control groups showed significantly higher fruit set rates compared to self-pollination treatments (Figure 3E), indicating a predominant reliance on outcrossing for progeny production under natural conditions. This species exhibits an outcrossing-dependent breeding system with self-compatibility, analogous to the reproductive traits of Actaea asiatica [59]. Furthermore, the absence of apomixis in I. jinggangensis necessitates obligate sexual reproduction requiring pollinator intervention to achieve high reproductive success.
All three Impatiens species share a pollination mechanism where primary pollinators land on the wing petals and access nectar through specialized pollination channels. Their zygomorphic floral symmetry features wing and labellum petals, functioning as “landing platforms”. In floral trait removal experiments, the presence of wing petals significantly affected fruit set rates in I. davidii and I. commelinoides (Figure 3A,C), whereas no significant impact was observed in I. jinggangensis. This suggests that pollinators of these species may rely on alternative floral traits for recognition. Upon selecting flowers, pollinators typically land on wing petals and probe nectar through the pollen tube. The absence of such “landing platforms” likely disrupts foraging behavior, consistent with findings that missing floral structures reduce the pollination efficiency [60].
The floral spur represents one of the most distinctive adaptations to pollinators. Generally, bumblebee (Bombus) foraging behavior correlates significantly with the proboscis length: species with longer proboscises preferentially visit plants with longer spurs, while those with shorter proboscises favor plants with shorter spurs [61]. I. davidii, which possesses the shortest spurs among the three species, exhibited the lowest diversity of observed pollinators. This pattern is consistent with observations in Angraecum orchids, where an increased spur length is associated with reduced pollinator diversity and selection for pollinators with longer proboscises [19,62,63,64]. Additionally, the spur length governs the nectar-storage capacity and differentiation in pollination syndromes [20,32]. Field measurements revealed that I. commelinoides produced the lowest nectar sugar content despite its relatively long spurs. I. jinggangensis, with the longest spurs, attracted one Bombus species characterized by the longest proboscises (Table 1), likely due to its sympatric distribution with I. davidii. However, proboscis–spur mismatches in these Bombus species hindered efficient nectar acquisition, resulting in reduced visitation rates. Furthermore, increasing the spur length inversely correlated with the primary pollinator visitation frequency, as elongated spurs elevated the foraging difficulty. Our findings corroborate the critical role of proboscis–spur matching in plant–pollinator interactions [32] and demonstrate that the visitation frequency variation is spur-length dependent.
Floral scent plays a pivotal role in pollinator attraction and mediates plant–pollinator coevolution [65,66,67]. Linalool, a key volatile organic compound, serves as a major attractant for Apidae bees, lepidopterans, and Macroglossum moths during pollination [68,69,70]. All three Impatiens species emitted linalool, with I. davidii exhibiting significantly higher mean concentrations. Although linalool acts as a generalized pollinator attractant, field observations revealed no corresponding expansion of floral visitor niches, potentially due to concentration-dependent effects: elevated linalool levels may suppress the visitation frequency [71]. As an aromatic compound, linalool is preferentially associated with sweet-taste perception in Bombus [72]. While direct evidence linking specific volatiles to pollinator preferences remains elusive. Our findings confirm that floral scent profiles modulate the visitation frequencies of key pollinators.

5. Conclusions

Our research indicates that the three Impatiens species demonstrated self-compatibility with predominant reliance on outcrossing, necessitating pollinator mediation for successful reproduction. While I. jinggangensis retained autonomous autogamy as an adaptive safeguard, spur length emerged as a critical modulator of the pollinator visitation frequency and functional guild composition. Interspecific variations in floral scent profiles further refined pollinator-mediated interactions. This comprehensive analysis of pollination dynamics and breeding systems revealed significant divergence in floral morphology and scent chemistry among forest understory Impatiens species, establishing their pivotal roles in structuring pollinator assemblages and shaping species-specific pollination strategies. These findings highlight the importance of integrating olfactory and morphological trait analyses when deciphering pollination mechanisms in understory angiosperms, offering critical insights for both conservation initiatives and ecological studies of pollination strategy differentiation in shaded ecosystems. Concurrently, this study establishes a novel methodological framework for investigating Impatiens species in understory ecosystems, focusing on integrated assessments of pollination mechanisms. Nevertheless, we acknowledge the limitations of our experimental design, particularly the lack of corroborative results from congeneric species across varied environmental conditions. Future studies will address this knowledge gap to advance our understanding of pollination dynamics in understory plant communities.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/horticulturae11050453/s1, Table S1: Comparative analysis of floral volatile organic compounds (VOCs) in three Impatiens species.

Author Contributions

Conceptualization, Q.S. and Y.X. (Yian Xiao); methodology, Y.X. (Yuxi Xue), Q.S. and L.L.; software, Y.X. (Yuxi Xue) and S.Z.; validation, Y.X. (Yuxi Xue), Q.S. and Y.X. (Yian Xiao); formal analysis, Y.X. (Yuxi Xue) and Y.Z.; investigation, H.L.; resources, Y.X. (Yian Xiao); data curation, Y.X. (Yuxi Xue), S.Z., Y.Z., H.L., L.L., J.Z. and W.H.; writing—original draft preparation, Y.X. (Yuxi Xue); writing—review and editing, Q.S. and Y.X. (Yian Xiao); visualization, Q.S. and Y.X. (Yian Xiao); project administration, Y.X. (Yian Xiao); funding acquisition, Y.X. (Yian Xiao). All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (42467035) and Key Laboratory of Jiangxi Province for Biological Invasion and Biosecurity (2023SSY02111).

Data Availability Statement

Data can be made available on reasonable request.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Lin, F.M.; Jiang, C.; Zeng, X.L.; Ren, Y.; Jin, Y.Q.; Feng, D.F.; Chen, Y.Y.; Liu, C.G.; Chen, S.J. Seasonal dynamics of understory vegetation diversity and biomass allocationa cross different tropical land use types. Acta Ecol. Sin. 2024, 44, 9379–9390. [Google Scholar]
  2. Liang, W.; Wei, X. Relationships between ecosystems above and below ground including forest structure, herb diversity and soil properties in the mountainous area of Northern China. Glob. Ecol. Conserv. 2020, 24, e01228. [Google Scholar] [CrossRef]
  3. Gilliam, F.S. The ecological significance of the herbaceous layer in temperate forest ecosystems. Bioscience 2007, 57, 845–858. [Google Scholar] [CrossRef]
  4. Wayman, R.B.; North, M. Initial response of a mixed-conifer understory plant community to burning and thinning restoration treatments. For. Ecol. Manag. 2007, 239, 32–44. [Google Scholar] [CrossRef]
  5. Nilsson, M.C.; Wardle, D.A. Understory vegetation as a forest ecosystem driver: Evidence from the northern Swedish boreal forest. Front. Ecol. Environ. 2005, 3, 421–428. [Google Scholar] [CrossRef]
  6. Gonzalez, M.; Augusto, L.; Gallet-Budynek, A.; Xue, J.; Yauschew-Raguenes, N.; Guyon, D.; Trichet, P.; Delerue, F.; Niollet, S.; Andreasson, F.; et al. Contribution of understory species to total ecosystem aboveground and belowground biomass in temperate Pinus pinaster Ait. forests. For. Ecol. Manag. 2013, 289, 38–47. [Google Scholar] [CrossRef]
  7. Fenster, C.B.; Armbruster, W.S.; Wilson, P.; Dudash, M.R.; Thomson, J.D. Pollination syndromes and floral specialization. Annu. Rev. Ecol. Evol. Syst. 2004, 35, 375–403. [Google Scholar] [CrossRef]
  8. Woźniak, N.J.; Sicard, A. Evolvability of flower geometry: Convergence in pollinator-driven morphological evolution of flowers. Semin. Cell Dev. Biol. 2018, 79, 3–15. [Google Scholar] [CrossRef]
  9. Abdusalam, A.; Liao, W.J.; Zhang, Z.Q.; Li, Q.J. Pollinator shifts along an elevation gradient mediate different response in self-pollination in heterostylous Primula nivalis. J. Syst. Evol. 2022, 60, 186–195. [Google Scholar] [CrossRef]
  10. Lehmann, L.J.; Maruyama, P.K.; Joaquim Bergamo, P.; Maglianesi, M.A.; Rahbek, C.; Dalsgaard, B. Relative effectiveness of insects versus hummingbirds as pollinators of Rubiaceae plants across elevation in Dominica, Caribbean. Plant Biol. 2019, 21, 738–744. [Google Scholar] [CrossRef]
  11. Toon, A.; Cook, L.G.; Crisp, M.D. Evolutionary consequences of shifts to bird-pollination in the Australian pea-flowered legumes (Mirbelieae and Bossiaeeae). BMC Evol. Biol. 2014, 14, 43. [Google Scholar] [CrossRef]
  12. Li, Q.X.; Zhang, M.R.; Gu, C.H.; Li, T.P.; Wan, Q.; Gao, L.; Zhang, T.Y.; Zhao, N.N.; Cai, Y.H. Floral syndrome and breeding system of Stewartia rostrata. J. Zhejiang AF Univ. 2022, 39, 830–837. [Google Scholar]
  13. Cao, M.H.; Zhao, Q.Y.; Wei, C.M.; Huang, H.Q.; Huang, M.J. Study on the flowering traits and breeding systems of three Impatiens species. Plant Sci. J. 2022, 40, 291–301. [Google Scholar] [CrossRef]
  14. Fan, X.L.; Barrett, S.C.; Lin, H.; Chen, L.L.; Zhou, X.; Gao, J.Y. Rain pollination provides reproductive assurance in a deceptive orchid. Ann. Bot. 2012, 110, 953–958. [Google Scholar] [CrossRef]
  15. Spigler, R.B.; Charles, A. Inbreeding reduces floral longevity and flower size in the mixed-mating biennial Sabatia angularis. Int. J. Plant Sci. 2023, 184, 157–163. [Google Scholar] [CrossRef]
  16. Shi, H.Y.; Wu, J.; Li, J.L.; An, J.D. Foraging preference of the bumblebee Bombus hypocrita (Hymenoptera: Apidae). Acta Entomol. Sin. 2008, 9, 946–952. [Google Scholar]
  17. Ruchisansakun, S.; Mertens, A.; Janssens, S.B.; Smets, E.F.; Van Der Niet, T. Evolution of pollination syndromes and corolla symmetry in Balsaminaceae reconstructed using phylogenetic comparative analyses. Ann. Bot. 2021, 127, 267–280. [Google Scholar] [CrossRef]
  18. Huang, Z.H. The Pollination System and Floral Evolution of Genus Rhododendron (Ericaceae). Ph.D. Thesis, Wuhan University, Wuhan, China, 2015. [Google Scholar]
  19. Luo, S.F.; Jiang, K.; Huang, W.C. Advances in the convergent evolution of phenotypes and diversification of developmental mechanisms of floral spurs. Biodivers. Sci. 2023, 31, 194–205. [Google Scholar] [CrossRef]
  20. Lu, G.M.; Lu, N.N.; Ma, Y.; Gao, C.F. Floral traits and their manipulation of foraging behaviors of pollinators of two sympatric Pedicularis species. J. Lanzhou Univ. Nat. Sci. 2021, 57, 338–343. [Google Scholar]
  21. Pyke, G.H. Floral nectar: Pollinator attraction or manipulation? Trends Ecol. Evol. 2016, 31, 339–341. [Google Scholar] [CrossRef]
  22. Zhang, Y.D.; Zhu, Y.; Li, Q.Q.; Wang, Y.C.; Tao, L.; Li, L. Pollination biology of two Chinese endemic and sympatric Impatiens (Balsaminaceae) species. Guihaia 2024, 44, 741–755. [Google Scholar] [CrossRef]
  23. Van der Niet, T.; Peakall, R.; Johnson, S.D. Pollinator-driven ecological speciation in plants: New evidence and future perspectives. Ann. Bot. 2014, 113, 199–212. [Google Scholar] [CrossRef]
  24. Van der Niet, T.; Johnson, S.D. Phylogenetic evidence for pollinator-driven diversification of angiosperms. Trends Ecol. Evol. 2012, 27, 353–361. [Google Scholar] [CrossRef] [PubMed]
  25. Dupont, Y.L.; Hansen, D.M.; Rasmussen, J.T.; Olesen, J.M. Evolutionary changes in nectar sugar composition associated with switches between bird and insect pollination: The Canarian bird-flower element revisited. Funct. Ecol. 2004, 18, 670–676. [Google Scholar] [CrossRef]
  26. Tong, Z.Y.; Huang, S.Q. Potential selection driving evolution of long corolla tubes and case studies. Plant Sci. J. 2023, 41, 719–728. [Google Scholar]
  27. Yu, S.X.; Janssens, S.B.; Zhu, X.Y.; Lidén, M.; Gao, T.G.; Wang, W. Phylogeny of Impatiens (Balsaminaceae): Integrating molecular and morphological evidence into a new classification. Cladistics 2016, 32, 179–197. [Google Scholar] [CrossRef] [PubMed]
  28. Yuan, T.H.; Li, M.J.; Ren, L.Y.; Huang, R.X.; Chen, Y.; Bai, X. A dataset on the diversity and geographical distributions of wild Impatiens in China. Biodivers. Sci. 2022, 30, 118–122. [Google Scholar] [CrossRef]
  29. Wang, J.S.; Lu, Y.F.; Xu, Y.L.; Jin, S.H.; Jin, X.F. Impatiens wuyiensis (Balsaminaceae), a new species from Fujian of Southeast China, based on morphological and molecular evidences. Bot. Stud. 2020, 61, 29. [Google Scholar] [CrossRef]
  30. Tiwari, U.L. Impatiens tajoensis (Balsaminaceae): A new species from Arunachal Pradesh, India. Taiwania 2023, 68, 39–43. [Google Scholar]
  31. Tian, J.; Yuan, T.H.; Peng, S.; Yang, Z.Z.; Hu, G.W.; Wang, Q.F. A new species of Impatiens (Balsaminaceae) from Southern Xizang, China with supplementary knowledge on I. leptocarpa Hook. f. Phytotaxa 2024, 661, 47–62. [Google Scholar] [CrossRef]
  32. Hořák, D.; Janeček, Š. A geographical perspective on the relationship between Impatiens spur lengths and bill lengths of sunbirds in Afrotropical mountains. Ecol. Evol. 2021, 11, 3120–3129. [Google Scholar] [CrossRef] [PubMed]
  33. Xiao, X.L. The Pollination Biology of Four Species of Impatiens L. Master’s Thesis, Hunan Normal University, Changsha, China, 2009. [Google Scholar]
  34. Zhong, Y.F.; Zhang, Z.; Song, X.Q.; Zhou, Z.D. Pollination biology of Impatiens hainanensis (Balsaminaceae) populations at different altitudes. Biodivers. Sci. 2014, 22, 467–475. [Google Scholar]
  35. Tian, J.; Liu, K.; Hu, G. Pollination ecology and pollination system of Impatiens reptans (Balsaminaceae) endemic to China. Ann. Bot. 2004, 93, 167–175. [Google Scholar] [CrossRef] [PubMed]
  36. Xiao, L.X.; Ming, K. Floral Traits Pollination System of Impatiens chinensis (Balsaminaceae). Bull. Bot. Res. 2009, 29, 164–168. [Google Scholar]
  37. Mao, Z.B.; Boehler, C.; Ge, X.J. Pollination ecology and breeding system of Impatiens lateristachys (Balsaminaceae) endemic to China. Guihaia 2011, 31, 160–166. [Google Scholar]
  38. Tang, Y.F.; Fang, Y.; Liu, C.Q.; Lu, Q.B.; Hu, X.H. The long spur of Impatiens macrovexilla may reflect adaptation to diurnal hawkmoth pollinators despite diversity of floral visitors. Flora 2020, 266, 151599. [Google Scholar] [CrossRef]
  39. Li, D.F.; Yan, X.C.; Lin, Y.; Wang, L.; Wang, Q. Do flowers removed of either nectar or pollen attract fewer bumblebee pollinators? An experimental test in Impatiens oxyanthera. AoB Plants 2021, 13, plab029. [Google Scholar] [CrossRef]
  40. Fischer, E.; Abrahamczyk, S.; Holstein, N.; Janssens, S.B. Evolution of Impatiens (Balsaminaceae) in the Albertine Rift-The endemic Impatiens purpureoviolacea complex consists of ten species. Taxon 2021, 70, 1273–1299. [Google Scholar] [CrossRef]
  41. Abrahamczyk, S.; Humphreys, A.M.; Trabert, F.; Droppelmann, F.; Gleichmann, M.; Krieger, V.; Linnartz, M.; Lozada-Gobilard, S.; Rahelivololona, M.E.; Schubert, M.; et al. Evolution of brood-site mimicry in Madagascan Impatiens (Balsaminaceae). Perspect. Plant Ecol. Evol. Syst. 2021, 49, 125590. [Google Scholar] [CrossRef]
  42. Wang, X.; Chen, Y.; Yi, Y. Features of floral odor and nectar in the distylous Luculia pinceana (Rubiaceae) promote compatible pollination by hawkmoths. Ecol. Evol. 2023, 13, e9920. [Google Scholar] [CrossRef]
  43. Mundi, O.; Awa Ii, T.; Chmel, K.; Ewome, F.L.; Uceda-Gómez, G.; Janečková, P.; Janeček, Š. The ornithophily of Impatiens sakeriana does not guarantee a preference by sunbirds. Biol. J. Linn. Soc. 2022, 137, 240–249. [Google Scholar] [CrossRef]
  44. Deng, X.L.; Liu, Y.C.; Wu, Y. Interconnection among dominant plant populations of Castanopsis community in Jinggang mountain nature reserve. Acta Phytoecol. Sin. 2003, 27, 531–536. [Google Scholar]
  45. Oksanen, J.; Blanchet, F.G.; Kindt, R.; Legendre, P.; Minchin, P.R.; O’hara, R.B.; Simpson, G.L.; Solymos, P.; Stevens, M.H.H.; Wagner, H. Community Ecology Package. R Package Version 2013, 2, 321–326. [Google Scholar]
  46. Ginestet, C. ggplot2: Elegant graphics for data analysis. J. R. Stat. Soc. Ser. A Stat. Soc. 2011, 174, 245–246. [Google Scholar] [CrossRef]
  47. Rossi, G.S.; Alaa, E.; Jerrica, J.; Kenneth, C.; Welch, J. Heat exposure limits pentose phosphate pathway activity in bumblebees. Conserv. Physiol. 2024, 12, coae031. [Google Scholar] [CrossRef]
  48. Huang, X.B.; Li, H.; Dai, X.Y.; Wu, G.A.; Zhou, H.; Chen, H.; Zheng, L.; Zhai, Y.F. Research Progress of Bumblebee Behavior and Pollination Application. Shandong Agric. Sci. 2021, 53, 130–137. [Google Scholar]
  49. Herrera, C.M. Components of pollinator “quality”: Comparative analysis of a diverse insect assemblage. Oikos 1987, 50, 79–90. [Google Scholar] [CrossRef]
  50. Kahnt, B.; Hattingh, W.N.; Theodorou, P.; Wieseke, N.; Kuhlmann, M.; Glennon, K.L.; van der Niet, T.; Paxton, R.; Cron, G.V. Should I stay or should I go? Pollinator shifts rather than cospeciation dominate the evolutionary history of South African Rediviva bees and their Diascia host plants. Mol. Ecol. 2019, 28, 4118–4133. [Google Scholar] [CrossRef]
  51. Kang, X.S.; Pan, B.; Duan, S.; Suo, F.Y.; Zhang, Y.Z.; Shi, W.; Gulnur, S. Comparison of Flowering Phenology and Reproductive Traits of Four Species of Calligonum L. (Polygonaceae) under Ex-situ Conservation at the Turpan Eremophytes Botanical Garden in Xinjiang. J. Desert Res. 2012, 32, 1315–1327. [Google Scholar]
  52. Hu, J.; Jiang, J.L.; Cheng, W.N.; Wei, L.N.; Wang, Y.; Hu, F.C.; Deng, X.X.; Li, Y. Pollination biology and breeding system of endangred plant Petrocosmea qinlingensis. Acta Ecol. Sin. 2024, 44, 8595–8604. [Google Scholar]
  53. Perazza, G.; Decarli, M. Monitoring of Cypripedium calceolus (Orchidaceae) in the Adamello-Brenta Natural Park (Italy). Nat. Conserv. Res. 2020, 5, 178–184. [Google Scholar] [CrossRef]
  54. Zhou, Z.L.; Li, Z.J.; Gong, W.S.; Gao, S. Study on the Flowering Phenology in Populus euphratica and Populus pruinosa. J. Wuhan Bot. Res. 2005, 23, 163–168. [Google Scholar]
  55. Charlesworth, D.; Brian, C. Inbreeding depression and its evolutionary consequences. Annu. Rev. Ecol. Syst. 1987, 18, 237–268. [Google Scholar] [CrossRef]
  56. Moore, D. Insects of palm flowers and fruits. In Insects on Palms; CABI: Wallingford, UK, 2001; pp. 233–266. [Google Scholar]
  57. Piao, J.; Ju, H.G.; Piao, Z.Y. Floral syndrome and breeding system of Atractylodes japonica. Guihaia 2015, 35, 166–172. [Google Scholar]
  58. Issaly, E.A.; Sersic, A.N.; Pauw, A.; Cocucci, A.A.; Traveset, A.; Benitez-Vieyra, S.M.; Paiaro, V. Reproductive ecology of the bird-pollinated Nicotiana glauca across native and introduced ranges with contrasting pollination environments. Biol. Invasions 2020, 22, 485–498. [Google Scholar] [CrossRef]
  59. Zhang, J.D.; Wang, L.; Sui, J.; Tian, X.H.; Ren, Y. Self-pollination Mechanism of Actaea asiatica (Ranunculaceae). CBB 2018, 53, 212–218. [Google Scholar]
  60. Del Carmen Salas-Arcos, L.; Lara, C.; Castillo-Guevara, C.; Cuautle, M.; Ornelas, J.F. “Pro-bird” floral traits discourage bumblebee visits to Penstemon gentianoides (Plantaginaceae), a mixed-pollinated herb. Sci. Nat. 2019, 106, 1. [Google Scholar] [CrossRef]
  61. Liang, H.; Zhao, Y.H.; Rafferty, N.E.; Ren, Z.X.; Zhong, L.; Li, H.D.; Li, D.Z.; Wang, H. Evolutionary and ecological factors structure a plant–bumblebee network in a biodiversity hotspot, the Himalaya–Hengduan Mountains. Funct. Ecol. 2021, 35, 2523–2535. [Google Scholar] [CrossRef]
  62. Micheneau, C.; Fournel, J.; Humeau, L.; Pailler, T. Orchid–bird interactions: A case study from Angraecum (Vandeae, Angraecinae) and Zosterops (white-eyes, Zosteropidae) on Reunion Island. Botany 2008, 86, 1143–1151. [Google Scholar] [CrossRef]
  63. Micheneau, C.; Fournel, J.; Warren, B.H.; Hugel, S.; Gauvin-Bialecki, A.; Pailler, T.; Strasberg, D.; Chase, M.W. Orthoptera, a new order of pollinator. Ann. Bot. 2010, 105, 355–364. [Google Scholar] [CrossRef]
  64. Minet, J.; Basquin, P.; Haxaire, J.; Lees, D.C.; Rougerie, R. A new taxonomic status for Darwin’s “predicted” pollinator: Xanthopan praedicta stat. nov. Antenor 2021, 8, 69–86. [Google Scholar]
  65. Huber, F.K.; Kaiser, R.; Sauter, W.; Schiestl, F.P. Floral scent emission and pollinator attraction in two species of Gymnadenia (Orchidaceae). Oecologia 2005, 142, 564–575. [Google Scholar] [CrossRef]
  66. Jürgens, A. The hidden language of flowering plants: Floral odours as a key for understanding angiosperm evolution? New Phytol. 2009, 183, 240–243. [Google Scholar] [CrossRef]
  67. Ramírez, S.R.; Eltz, T.; Fujiwara, M.K.; Gerlach, G.; Goldman-Huertas, B.; Tsutsui, N.D.; Pierce, N.E. Asynchronous diversification in a specialized plant-pollinator mutualism. Science 2011, 333, 1742–1746. [Google Scholar] [CrossRef]
  68. Kamatou, G.P.; Viljoen, A.M. Linalool-a review of a biologically active compound of commercial importance. Nat. Prod. Commun. 2008, 3, 1183–1192. [Google Scholar] [CrossRef]
  69. Raguso, R.A.; Pichersky, E.R. New Perspectives in Pollination Biology: Floral Fragrances. A day in the life of a linalool molecule: Chemical communication in a plant-pollinator system. Part 1: Linalool biosynthesis in flowering plants. Plant Spec. Biol. 1999, 14, 95–120. [Google Scholar] [CrossRef]
  70. Gong, W.C.; Xu, S.J.; Liu, Y.H.; Wang, C.M.; Martin, K.; Meng, L.Z. Chemical composition of floral scents from three Plumeria rubra L. (Apocynaceae) forms linked to petal color proprieties. Biochem. Syst. Ecol. 2019, 85, 54–59. [Google Scholar] [CrossRef]
  71. He, S.T. Gene Expression and Pollinator Response of Ordor Volatiles from Azadirachta indica Flowers. Ph.D. Thesis, Institute of Chemical Industry of Forest Products, Beijing, China, 2022. [Google Scholar]
  72. Galen, C. The effects of nectar thieving ants on seedset in floral scent morphs of Polemonium viscosum. Oikos 1983, 41, 245–249. [Google Scholar] [CrossRef]
Horticulturae 11 00453 g001
Figure 1. K−means clustering analysis of floral morphology in three Impatiens species.
Figure 1. K−means clustering analysis of floral morphology in three Impatiens species.
Horticulturae 11 00453 g001
Horticulturae 11 00453 g002
Figure 2. Pollen activity, ovule number, pollen number, nectar sugar content, and volume of three Impatiens species. Note: (A) the number of ovules of three Impatiens species; (B) the number of pollens of three Impatiens species; (C) the nectar content of three Impatiens species; (D) the nectar volume of three Impatiens species; (E–G) pollen Activity in three Impatiens species. Note: different letters represent significant differences.
Figure 2. Pollen activity, ovule number, pollen number, nectar sugar content, and volume of three Impatiens species. Note: (A) the number of ovules of three Impatiens species; (B) the number of pollens of three Impatiens species; (C) the nectar content of three Impatiens species; (D) the nectar volume of three Impatiens species; (E–G) pollen Activity in three Impatiens species. Note: different letters represent significant differences.
Horticulturae 11 00453 g002
Horticulturae 11 00453 g003
Figure 3. Seed number per capsule in the three Impatiens species influenced by the floral components and breeding system. Note: (A) the number of fruits removed from floral components of I. davidii; (B) the number of fruits removed from the floral components of I. jinggangensis; (C) the number of fruits removed from floral components of I. commelinoides; (D) the number of fruits under the breeding treatment of I. davidii; (E) the number of fruits under the breeding treatment of I. jinggangensis; (F) the number of fruits under the breeding treatment of I. commelinoides; combines box plots and violin plots. The central line in each box plot indicates the median, reflecting the central tendency of the dataset, while the box boundaries represent the upper quartile (Q3) and lower quartile (Q1). Note: different letters represent significant differences.
Figure 3. Seed number per capsule in the three Impatiens species influenced by the floral components and breeding system. Note: (A) the number of fruits removed from floral components of I. davidii; (B) the number of fruits removed from the floral components of I. jinggangensis; (C) the number of fruits removed from floral components of I. commelinoides; (D) the number of fruits under the breeding treatment of I. davidii; (E) the number of fruits under the breeding treatment of I. jinggangensis; (F) the number of fruits under the breeding treatment of I. commelinoides; combines box plots and violin plots. The central line in each box plot indicates the median, reflecting the central tendency of the dataset, while the box boundaries represent the upper quartile (Q3) and lower quartile (Q1). Note: different letters represent significant differences.
Horticulturae 11 00453 g003
Horticulturae 11 00453 g004
Figure 4. Floral visitation frequency patterns and major pollinator visitation in three species of Impatiens. (A) pollination frequency of I. davidii; (B) pollination frequency of I. jinggangensis; (C) pollination frequency of I. commelinoides; (D,G) main flower-visiting insects of I. davidii; (E,H) main flower-visiting insects of I. jinggangensis; (F,I) main flower-visiting insects of I. commelinoide.
Figure 4. Floral visitation frequency patterns and major pollinator visitation in three species of Impatiens. (A) pollination frequency of I. davidii; (B) pollination frequency of I. jinggangensis; (C) pollination frequency of I. commelinoides; (D,G) main flower-visiting insects of I. davidii; (E,H) main flower-visiting insects of I. jinggangensis; (F,I) main flower-visiting insects of I. commelinoide.
Horticulturae 11 00453 g004
Horticulturae 11 00453 g005
Figure 5. PCA and ANOSIM analyses of floral scents in three Impatiens species. Note: (A) PCA of floral scent profiles across three Impatiens species; (B) ANOSIM testing for interspecific divergence in the floral scent composition. Combines box plots and violin plots. The central line in each box plot indicates the median, reflecting the central tendency of the dataset, while the box boundaries represent the upper quartile (Q3) and lower quartile (Q1). Note: different letters represent significant differences.
Figure 5. PCA and ANOSIM analyses of floral scents in three Impatiens species. Note: (A) PCA of floral scent profiles across three Impatiens species; (B) ANOSIM testing for interspecific divergence in the floral scent composition. Combines box plots and violin plots. The central line in each box plot indicates the median, reflecting the central tendency of the dataset, while the box boundaries represent the upper quartile (Q3) and lower quartile (Q1). Note: different letters represent significant differences.
Horticulturae 11 00453 g005
Horticulturae 11 00453 g006
Figure 6. PCA analysis of pollination strategies in three Impatiens species.
Figure 6. PCA analysis of pollination strategies in three Impatiens species.
Horticulturae 11 00453 g006
Table 1. Plot information of three Impatiens populations.
Table 1. Plot information of three Impatiens populations.
SpciseCompanion PlantLongitude and LatitudeAltitude/m
I. davidiiRubus sp.1, Mallotus barbatus, Boehmeria platanifolia, Iris tectorum26.551850° N, 114.126558° E920
I. jinggangensisI. davidii, Equisetum hyemale, Lonicera japonica, Cnidium monnieri26.647942° N, 114.174698° E838
I. commelinoidesHypolepis punctata, Gonostegia hirta, Oenanthe javanica26.557789° N, 114.131217° E915
Table 2. Flowering phenology of three Impatiens species.
Table 2. Flowering phenology of three Impatiens species.
Blooming PeriodI. davidiiI. jinggangensisI. commelinoides
Flowering period of simple flower5.44 ± 0.25 d4.80 ± 0.4 d5.36 + 0.69 d
The stamen stage3.06 ± 0.14 d3.80 ± 0.89 d3.43 ± 0.24 d
Pistil stage2.39 ± 0.27 d1.00 ± 0.79 d1.93 ± 0.39 d
Full bloom stageSeptember–OctoberJuly–AugustJuly–August
Community flowering periodAugust–OctoberJune–OctoberJune–October
Fruit stageSeptember–NovemberAugust–NovemberJuly–November
Note: “d” is the standardized abbreviation for day(s).
Table 3. Analysis of three Impatiens species flower traits.
Table 3. Analysis of three Impatiens species flower traits.
Floral TraitsI. davidiiI. jinggangensisI. commelinoides
Symmetricalyesyesyes
GroupSection CrenaSection RacemusSection Laxiflora
Flower coloryellowredpurple
Length of dorsal petal13.23 ± 1.84 b11.58 ± 1.65 b17.34 ± 1.93 a
Width of dorsal petal11.85 ± 1.40 b9.38 ± 1.13 c14.00 ± 1.86 a
Height of channel6.22 ± 0.56 b7.65 ± 0.82 c6.67 ± 1.02 a
Depth of channel29.04 ± 3.47 b30.27 ± 4.24 b34.57 ± 4.17 a
Width of channel7.84 ± 0.96 a8.13 ± 0.76 a8.14 ± 0.77 a
Length of lateral sepal11.64 ± 1.18 a11.71 ± 1.00 a8.81 ± 1.02 b
Width of lateral sepal9.48 ± 1.35 a4.37± 0.46 c7.18 ± 0.81 b
Length of spur6.13 ± 1.05 c25.03 ± 6.00 a22.47 ± 3.51 b
Length of basal petal10.28 ± 1.45 b9.23 ± 1.92 b15.70 ± 2.77 a
Width of basal petal19.70 ± 2.80 b21.27 ± 5.64 a21.40 ± 3.06 a
Length of upper petal9.35 ± 1.72 a8.71 ± 2.85 a7.25 ± 0.97 a
Width of upper petal11.02 ± 3.63 b9.81 ± 2.31 b13.22 ± 1.51 a
Ring diameter length of spur1.53 ± 0.25 b1.58 ± 0.33 b1.72 ± 0.27 a
Corolla length18.29 ± 3.57 b27.25 ± 3.26 a26.95 ± 2.77 a
Protrusion of tongue12.34 ± 0.33 c27.47 ± 0.79 a19.33 ± 0.84 b
Body length18.16 ± 0.41 b18.28 ± 0.64 b16.42 ± 0.36 a
Breast height5.00 ± 0.13 a5.45 ± 0.29 a4.94 ± 0.09 a
Note: different letters represent significant differences.
Table 4. Plant characteristics of three Impatiens species.
Table 4. Plant characteristics of three Impatiens species.
SpeciesHeight\cmLeaf Length\mmLeaf Width\mmAspect RatioBasal Diameter\mm
I. davidii71.57 ± 24.05 b91.81 ± 18.29 b49.06 ± 12.31 a1.91 ± 0.26 b11.52 ± 3.95 b
I. jinggangensis107.15 ± 16.77 a126.47 ± 16.65 a37.02 ± 5.14 b3.43 ± 0.21 a15.5 ± 5.38 a
I. commelinoides52.7 ± 16.22 c43.37 ± 9.54 c22.91 ± 4.49 c1.9 ± 0.26 b2.65 ± 0.59 c
Note: different letters represent significant differences.
Table 5. Pollen number, ovule number, and ovule ratio in three Impatiens species.
Table 5. Pollen number, ovule number, and ovule ratio in three Impatiens species.
SpeciesPollen NumberOvule NumberOvule Ratio
I. davidii460,930.30 ± 81,977.65 a12.45 ± 3.34 a37,504.26 ± 6791.32 b
I. jinggangensis528,233.33 ± 126,452.9 a10.00 ± 0.8 9b52,918.13 ± 11,869.74 a
I. commelinoides186,485.00 ± 42,639.78 b9.75 ± 2.18 b17,141.79 ± 4152.89 c
Note: different letters represent significant differences.
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Xue, Y.; Su, Q.; Zhang, Y.; Zhang, S.; Li, H.; Liao, L.; Zeng, J.; Huang, W.; Xiao, Y. Reproductive and Pollination Characteristics of Three Understory Impatiens Species. Horticulturae 2025, 11, 453. https://doi.org/10.3390/horticulturae11050453

AMA Style

Xue Y, Su Q, Zhang Y, Zhang S, Li H, Liao L, Zeng J, Huang W, Xiao Y. Reproductive and Pollination Characteristics of Three Understory Impatiens Species. Horticulturae. 2025; 11(5):453. https://doi.org/10.3390/horticulturae11050453

Chicago/Turabian Style

Xue, Yuxi, Qitao Su, Yuxin Zhang, Shujian Zhang, Heng Li, Leiqin Liao, Jia Zeng, Weiyuan Huang, and Yian Xiao. 2025. "Reproductive and Pollination Characteristics of Three Understory Impatiens Species" Horticulturae 11, no. 5: 453. https://doi.org/10.3390/horticulturae11050453

APA Style

Xue, Y., Su, Q., Zhang, Y., Zhang, S., Li, H., Liao, L., Zeng, J., Huang, W., & Xiao, Y. (2025). Reproductive and Pollination Characteristics of Three Understory Impatiens Species. Horticulturae, 11(5), 453. https://doi.org/10.3390/horticulturae11050453

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop