Phylogeny and A Revised Classification of the Chinese Species of Nyssa (nyssaceae) Based on Morphological and Molecular Data

The taxonomy of Nyssa (Nyssaceae) in China is confused and uncertain due to differing views about how many species should be recognized, and a scarcity of good morphological differential characters. In the present study, we examined 52 morphological characters from up to fifty accessions each of six of the seven species recognized in the Flora of China: N. yunnanensis, N. javanica, N. sinensis, N. shangszeensis, N. shweliensis and N. wenshanensis. Based on both principal coordinate analysis and UPGMA cluster analysis, N. yunnanensis and N. javanica were both morphologically distinct. However, accessions of N. sinensis, N. shangszeensis, N. shweliensis and N. wenshanensis were intermixed in both analyses and could not be discriminated from each other. Sequence data from nuclear ITS and the chloroplast regions trnH-psbA, rps16r-f, trnL-rps32F, trnS-G and trnL-F were used to further analyze the Nyssa species listed above, together with N. aquatica and N. sylvatica from North America. All analyses of the DNA data using maximum parsimony, maximum likelihood and Bayesian methods strongly supported the monophyly of Nyssa. Within Nyssa, N. yunnanensis and N. javanica were resolved as sister species, which were genetically distinct. The other four Chinese taxa were barely differentiated by molecular data, with only N. shangszeensis and N. wenshanensis weakly supported as monophyletic. Hence, based on morphological and molecular data, we recommend that N. shangszeensis, N. shweliensis and N. wenshanensis be reduced to synonyms of N. sinensis, and only N. sinensis, N. yunnanensis and N. javanica be recognized for Flora of China. The American N. aquatica and N. sylvatica were sister species in the cpDNA but not in the ITS analyses, indicating possible reticulate evolution.