**2. Current Applications**

*2.1. Improving Taxonomy and Species Identification*

2.1.1. Defining Species Boundaries

Taxonomists have been using morphological features for the identification of both plants and animals since before the time of Carl von Linné. Yet, even after centuries of taxonomic work, perhaps only 20 percent of the species on Earth have been formally named [69]. Much work remains to be done. DNA barcoding provides a relatively new and significant tool to aid in the determination of species boundaries and discovery of new taxa. Entomologists have been pioneers in incorporating DNA barcode technologies for species discovery in the tropics, where the majority of biodiversity is found (e.g., [70–73]). Although the discriminatory power of barcode markers for plants is less than for insects, botanists have also used DNA barcodes as a taxonomic resource. Early studies, which have mostly focused on trees in tropical forest monitoring plots (e.g., [62,74,75]), demonstrated the difficulties of using DNA barcodes in plants (also see [76] for a recent study on African trees). However, the same studies also pointed out the advantages of being able to accurately identify sterile and juvenile specimens that lack morphological features required for identification. Costion et al. [77] applied a three-locus DNA barcode to estimate tree species diversity in a taxonomically poorly known tropical rain forest plot in Queensland, Australia, and concluded that DNA barcodes were a significant aid in rapid biodiversity assessment and determination of cryptic tree populations. A similar study in a central African rain forest plot recognized the high discriminatory power of barcode markers at the genus-level (95–100%), but somewhat lower species-level success (71–88%) in identification, especially in species-rich clades [78] or those with high rates of molecular evolution.

One of the major issues faced by plant taxonomists and ecologists attempting to use DNA barcodes in diverse forests, especially in the tropics, is that many species are new to science, therefore lack Latin binomials, and/or are members of poorly circumscribed species complexes that are difficult to identify even with traditional morphological data. Inventories and assessments of plant diversity in these habitats can be greatly enhanced by building DNA barcode libraries of these taxa [79]. Standardizing the DNA barcode markers and bioinformatics tools being used in different forest inventory projects (e.g., RAINFOR, http://www.rainfor.org/, accessed on 26 January 2022; the Amazon Tree Diversity Network [80], CForBio, http://www.cfbiodiv.org/, accessed on 26 January 2022; and ForestGEO [43]) will provide more confidence in identifications and maybe even allow rapid discovery and description of unknown taxa in these species-rich forests [79].

In addition to discovering new species, the introduction of integrative taxonomy has encouraged closer collaboration among biologists with different backgrounds, and in turn has promoted the use of DNA barcoding as a new tool in a broad taxonomic toolkit [81]. For very poorly documented regions or "understudied and hyperdiverse" taxa, DNA barcoding can be a key part of integrative workflows for species description and identification [82].
