The initial radiation of land vascular plants, as evidenced by the increase of both diversity and morphological disparity during the Silurian and Devonian periods, has been regarded as plant terrestrialization, which can be considered the equivalent in terrestrial environments of the Cambrian explosion of marine animals. Novel structures such as tracheids, stomata, leaves, roots and secondary xylem evolved during this time interval. However,how life-history strategies evolved in early land plants is not well understood.
As a predominant and typical component of Early Devonian floras, the Zosterophyllopsida has a long history of research, and was widely documented in palaeontology textbooks. This group appeared in the late Silurian and extended to the Late Devonian. Zosterophyllum has been reported around the world, especially in the South China Block, where at least 14 species of Zosterophyllum had been described. Some species are preserved as complete or nearly complete plants, such as Z. shengfengense. Thus, zosterophyllopsids are important material for the studies of life-history strategies of early land plants.
Recently, Dr. Pu Huang from the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, together with other collaborators, reported on a new species of Zosterophyllum, Z. baoyangense,from the Lower Devonian of Guizhou Province. Meanwhile, they built a multi-morphological-character dataset of the zosterophyllopsids from late Silurian to Early Devonian ages, and revealed the divergent life-history strategies in this group.
The plant bodyof the newly discovered Zosterophyllum baoyangense is ca 45.4 mm in whole length and its spikes are 5.8−10.8 mm high. The smaller body size with tiny spikes represents the smallest extreme among the early land plants.
Morphological characters of Zosterophyllum species and zosterophyllopsids were collected, including the width and length of axes, width and length of spikes as well as the sporangial height and width. Meanwhile, a new descriptor, total sporangial accommodation (TSA), was proposed to evaluate the mass or energy investment for spore production in each plant.
Pu Huang and his colleagues found that the length and width of axes generally follow the same trend of the diversity of species of Zosterophyllum, increasing from the Ludlow to Early Devonian, with the maximum range being reached in the Early Devonian. The TSA values and sporangial size of Zosterophyllum also show a similar pattern, with a huge different in vegetative and reproductive organ in Early Devonian. The minimum value of the TSA is represented by Z. baoyangense, only 4.3 to 16.8 mm3, while the TSA of Z. australianum is 29.6 to 499.0 mm3 occurred in the same bed of the Baoyang section. In additional, The TSA seems to be closely related to axial width. For the members of Lycophytina sensu Kenrick & Crane and Zosterophyllopsida sensu Hao & Xue, the length and width of axes generally follow the same trend of evolution.
The authors considered that highly morphologically diverse zosterophyllopsids in Pragian represent two groups in different life-history strategies. Like the r-selected species, one group is characterized by the smaller sizes and smaller TSA, shorter lifespan and lower vegetative and reproductive output, and seems to adapt to turbulent environment, such as Zosterophyllum baoyangense. The other group, such as Z. australianum, on the contrary to the former, like K-selected species. The authors argued that the transition from the Rhyniophytic Flora to the Eophytic Flora was probably driven by the evolution of divergent life-history strategies in Zosterophyllum and more broadly in zosterophyllopisds generally.
This work was financially supported by the National Key R&D Program of China and the National Natural Science Foundation of China. The authors include Dr. Pu Huang, and Dr. Jinzhuang Xue, Dr. Jiashu Wang (now at Geological Museum of China) and Mr. Yiling Wang from the Peking University,Dr. Lu Liu from the National Natural History Museum of China, and Dr. Jingyu Zhao from Suzhou University.
Article information: Huang,P.*,Wang,J.S.,Wang,Y.L.,Liu,L.,Zhao,J.Y.,Xue,J.Z.,2025. The smallest Zosterophyllum plant from the Lower Devonian of South China and the divergent life-history strategies in zosterophyllopsids. Proceedings of the Royal Society B 292: 20242337. https://royalsocietypublishing.org/doi/10.1098/rspb.2024.2337
Figure 1. Zosterophyllum baoyangense sp. nov., showing a fertile axis with K-shaped branching and a terminal spike. (The specimen was collected by Pu Huang, Lu Liu and Jinzhuang Xue in 2017)
Figure 2.Diversity and morphology of Zosterophyllum species through the late Silurian to Early Devonian. (a) Species richness;(b) Maximum length of axes; (c) Width of axes; (d) TSA; (e) Crossplot of sporangial width and height of different time bins; (f, g) Crossplot of TSA and axial width for all sampled Zosterophyllum species. (Data curation: Pu Huang, Yiling Wang; visualization: Jiashu Wang)
Figure 3. Artist’s restoration of part of the Early Devonian Mangshan flora, with plant communities of Zosterophyllum baoyangense at the front, and
Z. australianum and an unnamed plant to the back. (Conceptualization: Pu Huang; visualization: Chao Tan)
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