The early land plant fossils of the group zosterophyllopsid are widely recorded in global Silurian to Devonian sediments and acts as a dominant group in the Early Devonian flora of South China. Demersatheca contigua is an endemic zosterophyllopsid of the Early Devonian flora in South China and its paleophytogeographic implication to southern China Early Devonian is discussed.
Previous studies have suggested that the overall shape of the D. contigua is flat fern, while the new research changed this perception. In addition, the publication of D. contigua was effective but invalid because a holotype was not assigned in its initial description. Therefore, there are still many problems in the research of D. contigua.
Recently, the Devonian Investigation Group (DIG) of Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, led by Professors XU Honghe and WANG Yi and PhD student WANG Yao, researched the same species from the Lower Devonian layers from Guangxi and Yunnan. The plant fossils described in this study include 6 specimens previously attributed to Zosterophyllum contiguum or Z. australianum by Li and Cai from the Lower Devonian Posongchong Formation of Wenshan, Yunnan and 11 specimens newly collected from the Lower Devonian Cangwu Formation of Cangwu, Guangxi. A better understanding to the morphology of the zosterophyllopsid group is achieved with the examination of new specimens collected from these localities and the specimens previously reported. The study was online published recently in Review of Palaeobotany and Palynology.
The structure of the D. contigua strobilus is reconstructed and the diagnosis of the plant is emended in the aspect of four-row decussate sporangium arrangement. The nomenclature of D. contigua is summarized and the lectotype of the species is formally proposed.The strobilus of Demersatheca contigua is consists of four rows of lateral sporangia decussately arranged biconvex sporangia with marginal dehiscence bending towards the strobilus to make the strobilus a cylindrical-shape.
In this study, we according to the International Code of Nomenclature for Algae, Fungi, and Plants (Shenzhen Code), here propose to select the specimen from original materials as the lectotype of D. contigua. The lectotype in this case equates to the holotype.
For a long time, the southern China flora was thought to be a distinctive composition of the Early Devonian flora of China. However, recently accumulated study indicated that the Early Devonian flora of southern China can be subdivided into three phytogeographic zones, Yunnan, Guangxi and Sichuan, every flora of these three has its exclusive plant members, whilst a few shared members can be found among them. In generic level, Adoketophyton and Guangnania occur in both Yunnan and Sichuan; Demersatheca in Yunnan and Guangxi; Zosterophyllum in Guangxi, Yunnan and Sichuan. In specific level, only Demersatheca contigua occurs in Yunnan and Guangxi. These plant records, though being sparse and limited, seem to suggest similarities and potential relationships between these floras. A detailed flora comparison is highly expected and undoubtedly needed in the further study.
Reference: Wang Yao, Xu Hong-He*, Wang Yi, 2020. Morphology, nomenclature and potential paleophytogeographic implication of Demersatheca contigua (Zosterophyllopsida) from the Lower Devonian of Yunnan and Guangxi, southwestern China. Review of Palaeobotany and Palynology.104209. https://doi.org/10.1016/j.revpalbo.2020.104209
Fig. 1. Specimens of Demersatheca contigua (Zosterophyllopsida) from the Lower Devonian of Yunnan (A, B and E) and Guangxi (C and D), southwestern China.
Fig. 2. Three-dimensional diagram of the strobilus, the fertile structure of the Lower Devonian Demersatheca contigua (Zosterophyllopsida).
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