Congruent species delimitation of two controversial gold-thread nanmu tree species based on morphological and restriction site-associated DNA sequencing data

Species delimitation is fundamental to conservation and sustainable use of economically important forest tree species. However, the delimitation of two highly valued gold-thread nanmu species (Phoebe bournei and P. zhennan) has been confusing and debated. To address this problem, we integrated morphology and restriction site-associated DNA sequencing (RADseq) to define their species boundaries. We obtained highly consistent results from both data sets, supporting two distinct lineages corresponding to P. bournei and P. zhennan. In Phoebe bournei, higher order leaf venation is more prominent, petioles are thicker and leaf apex angle is narrower, compared to P. zhennan. Both data sets also showed that putative P. bournei localities from north-eastern Guizhou were P. zhennan. The two species have different distributions and only overlap in the Wuling Mountains. Phoebe bournei occurs mainly in Central Fujian, southern Jiangxi, the Nanling Mountains and the Wuling Mountains, whereas P. zhenn...