Phylogenetics of <i>Taxus</i> Using the Internal Transcribed Spacers of Nuclear Ribosomal DNA and Plastid <i>trnL-F</i> Regions
2020
Coughlan, Patricia | Carolan, James C. | Hook, Ingrid L. I. | Kilmartin, Lisa | Hodkinson, Trevor R.
<i>Taxus</i> is a genus of trees and shrubs with high value in horticulture and medicine as a source of the anticancer drug paclitaxel. The taxonomy of the group is complex due to the lack of diagnostic morphological characters and the high degree of similarity among species. <i>Taxus</i> has a wide global geographic distribution and some taxonomists recognize only a single species with geographically defined subgroups, whereas others have described several species. To address these differences in taxonomic circumscription, phylogenetic analyses were conducted on DNA sequences using Maximum Likelihood, Bayesian Inference and TCS haplotype networks on single and combined gene regions obtained for the nuclear ribosomal ITS region and the plastid <i>trnL</i> intron and <i>trnL-F</i> intergenic spacer. Evidence is presented for the sister group status of <i>Pseudotaxus</i> to <i>Taxus</i> and the inclusion of <i>Amentotaxus</i>, <i>Austrotaxus</i>, <i>Cephalotaxus</i> and <i>Torreya</i> within Taxaceae. Results are consistent with the taxonomic recognition of nine species: <i>T. baccata</i>, <i>T. brevifolia</i>, <i>T. canadensis</i>, <i>T. cuspidata</i>, <i>T. floridana</i>, <i>T. fuana</i>, <i>T. globosa</i>, <i>T. sumatrana</i> and <i>T. wallichiana,</i> but evidence is found for less species distinction and considerable reticulation within the <i>T. baccata</i>, <i>T. canadensis</i> and <i>T. cuspidata</i> group. We compare the results to known taxonomy, biogeography, present new leaf anatomical data and discuss the origins of the hybrids <i>T.</i> ×<i>media</i> and <i>T.</i> ×<i>hunnewelliana.</i>
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