DataSheet1_Refined Interpretation of the Pistillate Flower in Ceratophyllum Sheds Fresh Light on Gynoecium Evolution in Angiosperms.PDF

Molecular phylogenetic analyses have revealed a superclade of mesangiosperms with five extant lineages: monocots, eudicots, magnoliids, Ceratophyllum and Chloranthaceae. Both Ceratophyllum and Chloranthaceae are ancient lineages with a long fossil record; their precise placement within mesangiosperms is uncertain. Morphological studies have suggested that they form a clade together with some Cretaceous fossils, including Canrightia, Montsechia and Pseudoasterophyllites. Apart from Canrightia, members of this clade share unilocular gynoecia commonly interpreted as monomerous with ascidiate carpels. Alternatively, the gynoecium of Ceratophyllum has also been interpreted as syncarpous with a single fertile carpel (pseudomonomerous). We investigate patterns of morphological, anatomical and developmental variation in gynoecia of three Ceratophyllum species to explore the controversial interpretation of its gynoecium as either monomerous or pseudomonomerous. We use an angiosperm-wide morphological data set and contrasting tree topologies to estimate the ancestral gynoecium type in both Ceratophyllum and mesangiosperms. Gynoecia of all three Ceratophyllum species possess a small (sometimes vestigial) glandular appendage on the abaxial side and an occasionally bifurcating apex. The ovary is usually unilocular with two procambium strands, but sometimes bilocular and/or with three strands in C. demersum. None of the possible phylogenetic placements strongly suggest apocarpy in the stem lineage of Ceratophyllum. Rescoring Ceratophyllum as having two united carpels affects broader-scale reconstructions of the ancestral gynoecium in mesangiosperms. Our interpretation of the glandular appendage as a tepal or staminode homologue makes the Ceratophyllum ovary inferior, thus resembling (semi)inferior ovaries of most Chloranthaceae and potentially related fossils Canrightia and Zlatkocarpus. The entire structure of the flower of Ceratophyllum suggests strong reduction following a long and complex evolutionary history. The widely accepted notion that apocarpy is ancestral in mesangiosperms (and angiosperms) lacks robust support, regardless of which modes of carpel fusion are considered. Our study highlights the crucial importance of incorporating fossils into large-scale analyses to understand character evolution.

分子系统发育分析揭示了中果皮植物的一个总群，包括五个现存谱系：单子叶植物、双子叶植物、木兰科、Ceratophyllum和Chloranthaceae。Ceratophyllum和Chloranthaceae均为古老的谱系，具有悠久的化石记录；它们在中果皮植物中的确切位置尚不明确。形态学研究表明，它们与一些白垩纪化石，包括Canrightia、Montsechia和Pseudoasterophyllites，共同构成一个类群。除Canrightia外，该类群成员均具有单室雌蕊，通常被解释为单心皮且有裂果皮。另一种解释是，Ceratophyllum的雌蕊也被视为合心皮，具有单个可育心皮（假单心皮）。本研究旨在探讨Ceratophyllum三个物种雌蕊的形态、解剖和发育变异模式，以探讨其雌蕊作为单心皮或假单心皮的争议性解释。我们使用广域的被子植物形态数据集和对比的树形拓扑结构，来估计Ceratophyllum和中果皮植物中原始雌蕊的类型。三个物种的Ceratophyllum雌蕊在腹面均具有一个小（有时为退化的）腺体附属物，顶端偶尔呈二叉分裂。卵巢通常为单室，具有两个维管形成层，但在C. demersum中有时为双室和/或具有三个维管形成层。没有任何可能的系统发育位置强烈表明Ceratophyllum的茎源具有离生心皮。将Ceratophyllum重新评估为具有两个结合的心皮，会影响中果皮植物中原始雌蕊的更广泛规模的重建。我们将腺体附属物解释为花瓣或雄蕊同源物，使得Ceratophyllum的卵巢为下位，从而类似于大多数Chloranthaceae以及可能与Canrightia和Zlatkocarpus相关的化石的下位（半下位）卵巢。Ceratophyllum花朵的整个结构表明，其经历了漫长且复杂的进化历程后的显著退化。无论考虑何种心皮融合模式，被子植物（及有花植物）中离生心皮为原始形态的观点均缺乏强有力的支持。本研究强调了将化石纳入大规模分析以理解性状进化的关键重要性。（Generative AI）