**1. Introduction**

Algae in the order Trentepohliales are characterized by uniseriate and branched filaments. The order contains five genera and approximately 80 species that are primarily found in tropical and subtropical areas, and many of them form masses of a striking color (such as orange, yellow, and red) on tree trunks, walls, and stones [1]. Since the recorded species are completely aerial or subaerial, Trentepohliales is a special group in Ulvophyceae, of which the other groups are mainly composed of seaweeds or freshwater algae. The order can be easily distinguished from other

ulvophycean algae by its specific sporangiate-lateral. Other special morphological and ultrastructural features include the absence of pyrenoid in the net-like chloroplasts, plasmodesmata in the septa, and a phragmoplast similar to Streptophyta visible during cytokinesis [2]. As the type genus of Trentepohliaceae, *Trentepohlia* Martius is the earliest known and most studied. Several studies have confirmed that *Trentepohlia* are polyphyletic groups [3–6]. There are more than 46 valid *Trentepohlia* species recorded in AlgaeBase [1]. Among all the *Trentepohlia* species, *T. odorata* (F.H. Wiggers) Wittrock is a controversial species since several phycologists considered this species synonymous with *T. umbrina* or *T. iolithus*, whereas most phycologists treated *T. odorata* as valid separate species [7–10]. Moreover, the current molecular data (i.e., 18S rDNA, *rbcL* cpDNA) available has shown that several species in *Trentepohlia* are also polyphyletic, especially several widespread and common species, i.e., *T. arborum* and *T. umbrina* [5,6]. Additionally, the morphology and phylogenetic position of *Trentepohlia odorata* has rarely been reported.

Recent studies based on genome-wide data or multigene chloroplast data revealed that the Ulvophyceae is not monophyletic and was recovered as two or more distinct clades [11–13]. However, there are only several different chloroplast coding genes available in the database (i.e., GenBank), and no whole chloroplast genome of Trentepohliales has yet been reported. Chloroplasts in species of Ignatiales, Ulotrichales, Oltmannsiellopsidales, and Ulvales have been reported to share a similar structure with most Viridiplantae, of which the circular plastome was composed by two inverted repeat regions (IRa and IRb) and two single copy regions (LSC and SSC) [12,14–16]. The sequenced chloroplast genome of the BCDT clade (Bryopsidales, Cladophorales, Dasycladales and Trentepohliales) have unique plastome structures. For example, the chloroplast genome of a species of Cladophorales was reported to consist of 34 small hairpin chromosomes and lost many genes [17]. All available chloroplast genomes of Bryopsidales lack a large inverted repeat region [18,19]. In comparison with the relatives of Trentepohiales, there is little known about the evolution and chloroplast genome of the order. Thus, it is important to sequence the entire chloroplast genome of a species within Trentepohliales to increase our knowledge about the order.

During 2010–2016, we collected lots of Trentepohliacean specimens from China, as reported in previous study [5]. In the present study, we identified one corticolous specimen as *T. odorata* based on morphological evidence. Short- and long-read high-throughput sequencing data of this isolate were obtained and assembled. The aims of our study were: (1) to present the complete chloroplast genome of *Trentepohlia odorata*, (2) to study the taxonomy of *Trentepohlia odorata*, (3) to reconstruct phylogenetic relationship between *Trentepohlia odorata* and other species.
