Studies On Comparative Anatomy, Pollen Morphology And Molecular Phylogeny Of Desmos S.I.(Annonaceae)

As a genus of Annonaceae, Desmos s.1. includes Desmos Lour, and Dasymaschalon Dalle&Harms, which both have great academic and practical values. However, complexity of the taxonomic history and similar traits lead to the relationship between the two genera has long been controversial, and has caused taxonomic confusions. Using the experimental methods of comparative anatomy, palynology and molecular phylogenetics, and combining with the results of previous studies, we conducted a comprehensive study and discussion on the relationship between Desmos and Dasymaschalon for the first time.Leaf morphology in eight species of Desmos and seven species of Dasymaschalon was comparatively studied. There are many common characteristics between them, but these characteristics are frequently founded in Annonaceae. At the same time, significant differences in types of epidermal cells and crystals, distribution of oil cells and types of midrib vascular tissue were also founded between the two genera, considering these differences are useful for classification, the results supported the viewpoint that Desmos and Dasymaschalon should be treated as separate genera.Pollen grains in two sepecies of Desmos and two species of Dasymaschalon were examined by light microscope (LM) and scanning electron microscope (SEM). All species in this study have pollen grains with a strongly echinate exine, and there is almost no difference exist in shape and size between the two genera. But previous studies have showed that this pollen type also exists in other genera, and there are various pollen types in Dasymaschalon, nevertheless, Desmos has only one pollen type. So this study considered that Desmos is a natural genus, and supported the separation of them.A molecular phylogenetic study was conducted on seven species of Desmos and sixteen species of Dasymaschalon,by using sequences of three chloroplast DNA regions:psbA-trnH, matK and rbcL. The results showed that there are very close relationships among Desmos, Dasymaschalon and the outgroup Friesodielsia, but the relationships between Desmos and Friesodielsia, Dasymaschalon and Friesodielsia were not fully resolved base on the existing evidences. But in combination with the results of the study and the relevant literatures, considering that Desmos and Dasymaschalon are two ndependent groups, and Desmos is very natural, so the results supported them to be separated.With comprehensive consideration of the results in this study and combination of previous researches, the viewpoint of the study is that similar types in fruit and pollen grains can not well support for combining Desmos and Dasymaschalon as one genus, because the types also exist in their allied genera, in addition that there are visible differences between them, it was reasonable that they should be treated as two independent genera.