Pollen Morphology and Systematic Position of the Chinese Endemic Genus Dichotomanthes (Rosaceae)

Pollen morphology of the Chinese monotypic genus Dichotomanthes and its out-group Prinsepia utilis were investigated from the point of view of pollen development. The SEM observation revealed that there is not any change in morphology and sculpture of pollen grains from the young pollen grain seperated from callose of tetraspore to the mature pollen grain in Dichotomanthes tristaniaecarpa. Only the volume of pollen grain increased with maturity. In Prinsepia utilis, however, the appearance of pollen grains in young and mature stage varied a great deal. The mature pollen grains are amb 3-lobed circular, equatorial outline shaped as spheroidal, exine sculpture with parallel striate. The young ones, however, have a rather special appearance: amb 3-deep lobed circular and with the angulaperturate. The volume of pollen grain is much smaller than the mature with grains. Yet the exine sculpture is not very different between young and mature pollen grains. In these two species of Rosaceae, both show obvious variation in pollen volume between young and mature grains, but not much difference in exine sculpture. This reveals that the scupture date are one of the more reliable and stable characters compared with the pollen grain size. Dichotomanthes has the typical tricoporate pollen in Rosaceae. The exine structure is striate foveolate, and the pollen exine can be divided into tectume, columellae and foot layer. Comparing the palynological data with the four subfamilies under Rosaceae, together with the morphology and cytology data, we approve treating Dichotomanthes as a primitive genus in Maloideae, but reject placing it in Prunoideae or isolating it as a subfamily. In addition, since Prinsepia utilis has angulaperturate pollen grains in the early stage of pollen development and shars the same character with two taxa Geissois montana and Cunonia capensis under Cunoniaceae, the pollen morphological data supports the viewpoint that Rosaceae may have a systematic relationship with Cunoniaceae under Saxifragales.