Background and Aims Floral developmental studies are crucial for understanding the evolution of floral structures and sexual systems in angiosperms. Within the monocot order Poales, both subfamilies of Eriocaulaceae have unisexual flowers bearing unusual nectaries. Few previous studies have investigated floral development in subfamily Eriocauloideae, which includes the large, diverse and widespread genus Eriocaulon. To understand floral variation and the evolution of the androecium, gynoecium and floral nectaries of Eriocaulaceae, we analysed floral development and vasculature in Eriocaulon and compared it with that of subfamily Paepalanthoideae and the related family Xyridaceae in a phylogenetic context. Methods Thirteen species of Eriocaulon were studied. Developmental analysis was carried out using scanning electron microscopy, and vasculature analysis was carried out using light microscopy. Fresh material was also analysed using scanning electron microscopy with a cryo function. Character evolution was reconstructed over well-resolved phylogenies. Key Results Perianth reductions can occur due to delayed development that can also result in loss of the vascular bundles of the median sepals. Nectariferous petal glands cease development and remain vestigial in some species. In staminate flowers, the inner stamens can emerge before the outer ones, and carpels are transformed into nectariferous carpellodes. In pistillate flowers, stamens are reduced to staminodes and the gynoecium has dorsal stigmas. Conclusions Floral morphology is highly diverse in Eriocaulon, as a result of fusion, reduction or loss of perianth parts. The nectariferous carpellodes of staminate flowers originated first in the ancestor of Eriocaulaceae; petal glands and nectariferous branches of pistillate flowers originated independently in Eriocaulaceae through transfer of function. We present a hypothesis of floral evolution for the family, illustrating a shift from bisexuality to unisexuality and the evolution of nectaries in a complex monocot family, which can contribute to future studies on reproductive biology and floral evolution in other groups.

中文翻译：

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Eriocaulon（Eriocaulaceae）的花卉发育和脉管系统提供了对 Poales 进化的见解

背景和目的 花发育研究对于理解被子植物的花结构和性系统的进化至关重要。在单子叶植物 Poales 中，Eriocaulaceae 的两个亚科都有单性花，带有不寻常的蜜腺。很少有以前的研究调查过 Eriocauloideae 亚科的花发育，其中包括大型、多样化和广泛分布的 Eriocaulon 属。为了了解刺桐科的花变异和雄蕊、雌蕊和花蜜腺的进化，我们分析了刺桐的花发育和脉管系统，并在系统发育背景下将其与 Paepalanthoideae 亚科和相关的 Xyridaceae 进行了比较。方法对13种毛茛属植物进行研究。使用扫描电子显微镜进行发育分析，使用光学显微镜进行脉管系统分析。还使用具有低温功能的扫描电子显微镜对新鲜材料进行了分析。特征进化是在很好解决的系统发育上重建的。主要结果 花被减少可能是由于延迟发育而导致的，这也可能导致中间萼片的维管束丢失。在某些物种中，蜜腺花瓣腺停止发育并保持退化。在雄蕊花中，内部雄蕊先于外部雄蕊出现，心皮转化为含蜜的心皮。在雌蕊花中，雄蕊退化为退化雄蕊，雌蕊有背柱头。结论 Eriocaulon 的花形态高度多样化，是花被部分融合、减少或丢失的结果。雄花的蜜汁心皮最早起源于牛蒡科的祖先；雌花的花瓣腺和蜜腺分枝通过功能转移独立起源于毛茛科。我们提出了一个家庭的花进化假说，说明了从双性恋到单性恋的转变以及复杂单子叶植物家族中蜜腺的进化，这有助于未来对其他群体的生殖生物学和花进化的研究。