DataSheet2_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生胚植物中的一支超级类群，包含五个现存的谱系：单子叶植物、双子叶植物、木兰目、C. ceratophyllum 和 Chloranthaceae 科。C. ceratophyllum 和 Chloranthaceae 科均为古老的谱系，具有悠久的化石记录；它们在中生胚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 形成一个类群。除了 Canrightia 外，该类群成员共享单室雌蕊，通常被解释为单心皮且有裂果皮的。另一方面，C. ceratophyllum 的雌蕊也被解释为合心皮，具有单一有繁殖能力的子房（假单心皮）。本研究旨在探究三种 C. ceratophyllum 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。我们利用一个被子植物广泛形态数据集和对比的树形结构，估计了 C. ceratophyllum 和中生胚植物中祖先雌蕊的类型。三种 C. ceratophyllum 物种的雌蕊在腹面侧均具有一个小（有时退化）的腺体附属物和偶尔二叉的顶端。子房通常为单室，具有两条维管束，但在 C. demersum 中有时为双室或具有三条维管束。没有任何可能的系统发育位置强烈暗示 C. ceratophyllum 的茎系具有离生果。将 C. ceratophyllum 重新评估为具有两个联合的子房，影响了中生胚植物中祖先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 C. ceratophyllum 的子房为下位，从而类似于大多数 Chloranthaceae 以及潜在的相关化石 Canrightia 和 Zlatkocarpus 的（半）下位子房。C. ceratophyllum 花的整体结构表明，在经历了漫长而复杂的进化历程后，其结构发生了显著退化。无论考虑何种子房融合模式，被广泛接受的离生果是中生胚植物（和被子植物）祖先的观点都缺乏强有力的支持。本研究强调了将化石纳入大规模分析中，以理解性状进化的至关重要的意义。