Rhamnella intermedia, a new evergreen species from southwest Guangxi, is described and illustrated in this study. This species is similar to R. brachycarpa by the size and ratio of length to width of dried fruit and seeds, by which it differs from R. rubrinervis and R. tonkinensis. However, it differs from R. brachycarpa by rarely mucronate seed apices, larger ratio of length to width of leaves, leaf apices acuminate to long acuminate, shorter leaf petioles, and longer fruiting pedicels. Principal component analysis based on phenotypic traits further recognised three separated groups. Rhamnella rubrinervis and R. tonkinensis were clustered into one group; the other two groups represented R. brachycarpa and two Guangxi populations, respectively. Furthermore, phylogenetic analysis of nuclear ITS sequence variations highly supported that the two Guangxi populations represented an independent evolutionary lineage and were closest to R. rubrinervis. Four fixed nucleotide sites were found and were different from R. rubrinervis. However, besides the differentiated traits in seeds and fruit, densely pilose young branches also separated them from R. rubrinervis. In addition, during our field investigations, none of the three closely related species were found at locations where this new species was distributed. Therefore, this new species, based on the two Guangxi populations, is named R. intermedia. The key to four closely related species is also presented.
Keywords: Rhamnella; evergreen species; independent evolutionary lineage; intermediate morphology; phenotypic cluster.
Zhiqiang Lu, Yongshuai Sun.