被子植物 z-bo 2023-01-31 887

　　The origin and early evolution of angiosperms have been a difficult problem that botanists have worked hard to overcome for a long time. The way to solve this problem is to find fossil evidence. The Yixian Formation in western Liaoning in my country is famous for its angiosperm fossils. Recently, the academia has made progress on the paleobotanical research of the Yixian Formation, which is an angiosperm fossil.

　　The research team of Wang Xin, a researcher at the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, and his collaborators published online on Historical Biology entitled A novel angiosperm including various parts from the Early Cretaceous sheds new light on flower evolution ("Early Cretaceous sheds new light on flower evolution" New angiosperms provide new enlightenment for flower evolution"), reporting angiosperm fossils—Varifructus lingyuanensis, produced in the Zhangziyixian Formation of the Great King of Lingyuan, Liaoning (about 125 million years ago). Lingyuan Bianguo became the newest member of the early Cretaceous Yixian Formation angiosperm family after numerous angiosperms previously reported.

　　Lingyuan Bianguo is a large fossil preserved as positive and negative. The preserved part of the plant is about 17 cm high and 12 cm wide. The fossil preserves the end of the plant, including stems, leaves, flower buds, fruits and other connected organs. The leaf characteristics of Lingyuan Bianguo indicate that Lingyuan Bianguo cannot be a monocot. Although similar dicot leaves have been reported in fossil plants of the Yixian Formation, the properties of their parent plants have been undecided due to their separate preservation. The leaves of the fossil discovered this time are directly connected to other organs, providing an important window into the early angiosperm morphology.

　　Compared with the reported angiosperm fossils from the Yixian Formation, the biggest feature of Lingyuan Variety Fruit is "change", which is manifested in the following three aspects: (1) Leaf morphology: Two different types can be seen in the same fossil The leaves, near the base of the fossil, have two leaves, which have obvious slender petioles, and the leaves are deeply divided into two parts; in contrast, the leaves near the top fruits lack obvious petioles, and the leaves are only sunken at the edges. (2) Branching method: In the same fossil, Lingyuan Variety Fruit has opposite and non-opposite leaf axillary branches. (3) Morphological structure of fruit sequence: The fruit sequence of variable fruit is generally in pairs, but these two adjacent fruit sequences have different morphologies, one includes multiple fruit rounds, and gathers in a short and thick fruit. On the stalk; the other has only one or two fruits, growing on a slender stalk. These characteristics vary widely. If placed in a modern plant, they may cross the boundaries of different families and genus, and they appear in the same plant (Lingyuan change fruit), which fully shows that the early angiosperms have plasticity and morphology. Instability.

　　Lingyuan change fruit is of great significance to the evolution of flowers. Studies have found that the reproductive organs of Lingyuan Fruit on the same fossil are at different development stages, which is helpful for the academic community to understand the flower morphology and development process of the plant. The youngest reproductive organ of Lingyuan Variety Fruit is a flower bud with a truncated top, which seems to be wrapped in a perianth; its most mature reproductive organ is a relatively mature infructescence, including two or more clustered fruits. Since tepal-like structures are rarely seen in the plants of the Yixian group that have been reported, the tepal-like structures wrapped around the buds of Lingyuan Mutant fruit showed the embryonic petals for the first time.

　　In addition, the discovery of Lingyuan's change fruit also has important theoretical significance, and its ovule is born on the back suture of the fruit. This finding does not support the megaspore leaf theory popular in textbooks. According to this theory, the ovule should be born on the ventral suture of Lingyuan's transformed fruit. In terms of the location of the ovule, the Lingyuan variant fruit is consistent with the early angiosperm fossils (including ancient fruit and pseudo-herringbone) found in the Yixian Formation and the ancient flowers of the mid-Cretaceous in the United States. Plant characteristics do not support the megaspore theory, but they are all within the expectations of the newly proposed unified theory of plant evolution.