Abstract The pollen of Trigonostemon and the related genera Dimorphocalyx, Ostodes, Tritaxis and Jatropha (outgroup) has been studied with light microscopy, and scanning and transmission electron microscopy. The two major pollen types within Trigonostemon correlate well with macromorphological characters. Species belonging to the Trigonostemon reidioides type have pollen with ‘croton pattern’ ornamentation, a pistil with deeply divided stigmas (to at least half the length of the stigma arm) and stamens with a protruding appendage on the connective, while species of the Trigonostemon verrucosus type have verrucate (to almost gemmate) pollen, stigmas that are shortly cleft and stamens without an appendage on the connective. Dimorphocalyx, Ostodes, Tritaxis and Jatropha (outgroup) have similar pollen morphology, while Trigonostemon deviates from these genera in the absence of the ‘vertically’ striate ornamentation on the subunits. Therefore, when compared with an existing phylogeny of the Euphorbiaceae, the pollen characters of Trigonostemon appear to be derived. Moreover, because the ‘croton pattern’ ornamentation itself is widely shared by the ‘inaperturate crotonoids’, the loss of that structure in the Trigonostemon verrucosus type pollen is considered a further apomorphy.

中文翻译：

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Trigonostemon 及其近缘（大戟科）的花粉形态

摘要 用光学显微镜、扫描和透射电子显微镜研究了Trigonostemon 及其相关属Dimorphocalyx、Ostodes、Tritaxis 和Jatropha（外群）的花粉。Trigonostemon 内的两种主要花粉类型与宏观形态特征密切相关。属于 Trigonostemon reidioides 类型的物种具有带有“巴豆图案”装饰的花粉，具有深裂柱头（至少达到柱头臂长度的一半）的雌蕊和在连接处具有突出附属物的雄蕊，而 Trigonostemon verrucosus 的物种类型有疣状（几乎是成对的）花粉、短裂的柱头和在结缔组织上没有附属物的雄蕊。Dimorphocalyx、Ostodes、Tritaxis 和 Jatropha（外群）具有相似的花粉形态，而 Trigonostemon 在亚基上没有“垂直”条纹装饰的情况下偏离了这些属。因此，与大戟科的现有系统发育相比，Trigonostemon 的花粉特征似乎是衍生出来的。此外，由于“巴豆图案”装饰本身被“无孔巴豆”广泛共享，因此疣状花粉中该结构的丧失被认为是进一步的异形。