ON THE SYSTEMATIC POSITION OF GENUS DIPENTODON DUNN
Liu Jiansheng Cheng Chingyung(Beijing Medical University, Beijing, 100083)
In this paper, a comprehensive study on the morphological features of Dipentodon has been tried and comparisons were made with all the 17 related genera belonging to 6 families. The conclusions are as follows:(1) In Dipentodon, the inflorescence is an umbellate cyme instead of an umbel; the 10 perianth segments can be distinctly seen forming inner and outer whorls, with stamen opposited to the outer one; the disc is shallow at base and deeply clefted with 5—6(7) projecting lobes without glandular structure; there are two ovules within each of the three incomplete locules with only one of the six developing into Seed, meanwhile, the plancenta is elongated and forming a conspicuous stalk under the seed; these lead to the conclusion that morphologically Dipentodon is closely related to family Celastraceae.(2) Though some taxonomical characters of Dipentodon, such as perianth arrangement, articulated pedicels and tricolporate pollen grains resemble those in genera of Flacourtiaceae, characters in floral morphology, anatomy are all tremendously divergent, especially the placentation type, hence the posibility of close relationship between the two taxa is eliminated.(3) The anatomical characters of Dipentodon are similar with those of Hamamelidaceae but other characters are very different. (4) Resemblance in morphological, anatomical and palynological characters is found with those of Styraeaceae, yet the floral stucture and fruit feature discourage the concept of any colose relation between the two taxa.(5) The discrepancy in the morphological, anatomical and palynological characters with those of santales are too great to consider them close with Dipentodon in spite of the similarity of some plancental structures.(6) A new species of Dipentodon, D. longipedicellatus is described.(7) Dunn's treatment of family relation is supported here. The position of Dipentodon within Celastraceae is reviewed and a new subfamily——Dipen. todontoideae is set up. It is placed between Subfamilies Celastroideae and Tripterygioideae.