Hedyosmum-Like Fossils in the Early Cretaceous Diversification of Angiosperms
Hedyosmum-Like Fossils in the Early Cretaceous Diversification of Angiosperms
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DOI：
10.1086/701819
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发表时间：
2019-03-01
影响因子：
2.3
通讯作者：
Pedersen, Kaj Raunsgaard
中科院分区：
文献类型：
--
作者：
Friis, Else Marie;Crane, Peter R.;Pedersen, Kaj Raunsgaard
研究的前提。早期白垩纪类似白花蛇舌草的化石很重要，因为它们提供了产生海星花粉的植物的雌花和果实的信息，这种花粉在被子植物的历史上很早就很常见和广泛分布。白花蛇舌草属(Chloranthaceae)也是现存的唯一一个在被子植物演化的早期阶段就存在可信化石的属。方法：从松散的沉积物中筛选出化石，并用HF、HCl和水进行净化。利用扫描电子显微镜和同步辐射X射线断层扫描显微镜对其外部形态和内部解剖结构进行了研究。研究结果表明，葡萄牙早白垩世海星花粉附着于雌花和果实上，为白花蛇舌草类化石提供了新的信息。这些化石被归属于一个新的早白垩世分类群--Hedyflora Crystal alvena，其外部形态与现存的Hedyosum非常相似。然而，这些化石与现存属的不同之处在于，它们具有结晶的内被片，细胞具有内网状填充，这是除Hedyosum以外的所有现存金莲科的特征。现存的白花蛇舌草有一层薄的、未特化的种皮。这一新发现证实了早先的预测，即内胚层种皮是整个金莲科的祖先，但在导致现存白花蛇舌草的谱系中已经消失。结论：白花蛇舌草证实了白花蛇舌草谱系在被子植物辐射非常早期就与其他金莲科植物的分化，但驳斥了这些早期化石，认为这些早期化石是白垩纪早期白花蛇舌草存在的证据。
Premise of research.Early Cretaceous Hedyosmum-like fossils are important because they provide information on the pistillate flowers and fruits of plants that produced Asteropollis pollen, which is common and widely distributed very early in the history of angiosperms. Hedyosmum (Chloranthaceae) is also the only extant genus for which there is a plausible fossil presence at such an early stage of angiosperm evolution.Methodology.The fossils were sieved out of unconsolidated sediments and cleaned with HF, HCl, and water. External morphology and internal anatomy were studied using scanning electron microscopy and synchrotron radiation X-ray tomographic microscopy.Pivotal results.New information on Hedyosmum-like fossils is provided based on pistillate flowers and fruits with adhering Asteropollis pollen from the Early Cretaceous of Portugal. The fossils are assigned to a new Early Cretaceous taxon, Hedyflora crystallifera, which in external morphology is closely similar to extant Hedyosmum. However, the fossils differ from the extant genus in having a crystalliferous endotesta with cells that have endoreticulate infillings, a feature characteristic of all extant Chloranthaceae except Hedyosmum. Extant Hedyosmum has a thin, unspecialized seed coat. This new discovery confirms earlier predictions that an endotestal seed coat is ancestral for Chloranthaceae as a whole but has been lost in the lineage leading to extant Hedyosmum.Conclusions.Hedyflora confirms the divergence of the Hedyosmum lineage from other Chloranthaceae very early in the angiosperm radiation but refutes these early fossils as evidence of extant Hedyosmum in the Early Cretaceous.