Using DNA sequence data to enhance understanding and conservation of plant diversity at the species level

Understanding and conserving plant diversity is a pressing global challenge. In this chapter we explore the uses of genetics to enhance understanding of plant species diversity. Specifically we provide an overview of the use of genetic data for discriminating among plant species, ranging from broad-brush DNA barcoding studies to in-depth investigations of closely related species complexes. We highlight the types of data required to provide insights into differing levels of biological complexity and also explore future opportunities for further upscaling the use of genetic data at the species level in plants. The Use of Genetics to Tell Species Apart Characterisation of the world’s species is an enormous undertaking. Across eukaryotic life, estimates of species numbers vary greatly but with widespread acceptance that only a fraction of the species on Earth have yet been described (Mora et al., 2011). The situation is most acute for insects, where recent estimates suggest that the number of species may be as high as 10 million (Hebert et al., 2016a, b). In plants, the outstanding task is more manageable, but still substantial. Recent extrapolations suggest something in the order of 350,000-450,000 species of flowering plants (Pimm and Joppa, 2015), with estimates of c.70,000 species still awaiting discovery and description (Bebber et al., 2010). The mean time lag between species collection and species description is > 30 years, and about 50 per cent of the plant species awaiting discovery are considered to have already been collected and housed in herbaria (Bebber et al., 2010). Major outstanding challenges include quantification of diversity in the species-rich understudied regions of the planet, understanding diversity in large complicated genera, and reconciliation of species accounts between different geographical regions. Parallel to the challenge of plant species characterisation is plant identification. There is a general shortage of taxonomists and field biologists and even when experts are working on well-studied groups in well-studied regions, challenges remain when identification is required from sub-optimal material. Understanding regeneration patterns in species-rich systems requires identification of seedlings and juveniles - a non-trivial challenge in many long-lived taxa. Likewise, understanding food webs, pollination networks, below ground spatial architecture of roots, etc. all involve identification of plant parts that may lack the distinguishing characters used in taxonomic accounts.