State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing, China.
Chicago Botanic Garden, Glencoe, IL, USA.
Nature. 2021 Jun;594(7862):223-226. doi: 10.1038/s41586-021-03598-w. Epub 2021 May 26.
The second integument of the angiosperm ovule is unique among seed plants, with developmental genetics that are distinct from those of the inner integument. Understanding how the second integument should be compared to structures in other seed plants is therefore crucial to resolving the long-standing question of the origin of angiosperms. Attention has focused on several extinct plants with recurved cupules that are reminiscent of the anatropous organization of the basic bitegmic ovules of angiosperms, but interpretations have been hampered by inadequate information on the relevant fossils. Here we describe abundant exceptionally well-preserved recurved cupules from a newly discovered silicified peat dating to the Early Cretaceous epoch (around 125.6 million years ago) in Inner Mongolia, China. The new material, combined with re-examination of potentially related fossils, indicates that the recurved cupules of several groups of Mesozoic plants are all fundamentally comparable, and that their structure is consistent with the recurved form and development of the second integument in the bitegmic anatropous ovules of angiosperms. Recognition of these angiosperm relatives (angiophytes) provides a partial answer to the question of angiosperm origins, will help to focus future work on seed plant phylogenetics and has important implications for ideas on the origin of the angiosperm carpel.
被子植物胚珠的第二层珠被在种子植物中是独一无二的，其发育遗传学与内珠被的发育遗传学明显不同。因此，了解第二层珠被应该如何与其他种子植物的结构进行比较，对于解决被子植物起源的长期存在的问题至关重要。人们关注了几种具有内折杯状结构的已灭绝植物，这些植物让人联想到被子植物基本的合点双珠被的倒生组织，但由于相关化石的信息不足，解释受到了阻碍。在这里，我们描述了来自中国内蒙古早白垩世（约 1.256 亿年前）新发现的硅化泥炭中大量保存异常完好的内折杯状结构。新材料与可能相关化石的重新检查表明，中生代植物的几个类群的内折杯状结构在根本上是可比的，其结构与被子植物合点双珠被中的倒生胚珠的第二层珠被的内折形式和发育一致。这些被子植物亲缘关系（angiophytes）的识别为被子植物起源问题提供了部分答案，有助于将未来的工作重点放在种子植物系统发育上，并对心皮起源的观点具有重要意义。
