中国特有属牛筋条属的花粉形态与其系统位置

从发育的角度研究了中国特有单种属DichotomanthesKurz及与其系统学研究有关的外类群Prinsepiautilis的花粉形态 ,扫描电镜观察显示Dichotomanthes花粉粒自脱离四分体胼胝质膜开始至成熟二核花粉粒不同发育时期 ,花粉形态和外壁纹饰未见变化 ,仅花粉体积随成熟度增加而有所增大。而Prinsepiautilis ,其花粉粒刚脱离四分体时形状和成熟花粉明显不同 ,成熟花粉极面观为三裂圆形 ,赤道面观为圆形 ,外壁具清晰的平行条纹 ,但幼嫩花粉粒的形状很特别 ,极面观为深三裂圆形 ,赤道面观亦见花粉在两条沟之间下陷而沟部外突 ,明显为角萌发孔花粉 ,且花粉体积较成熟者小 ,而外壁纹饰同成熟者相比无根本性差异。前述两种植物花粉在不同成熟期体积有明显差异 ,而外壁纹饰在不同成熟期不存在质的变化并相对稳定 ,说明花粉外壁纹饰这一性状在蔷薇科中具有较为重要的分类学意义。DichotomanthesKurz具典型Rosaceae花粉的三孔沟结构 ,外壁具条纹 -穴状纹饰。将其孢粉学特征同Rosaceae 4个亚科有关类群的同类资料相比较 ,并结合其它形态解剖与细胞学等研究结果 ,支持将Dichotoman thes置入Maloideae下而不赞同将其另立亚科或置于Prunoideae之下。此外 ,由于Prinsepiautilis的花粉在其发育初期具角萌发孔花粉 ,与Cunoniacea

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.