Demersatheca Li et Edwards, gen. nov., a new genus of early land plants from the Lower Devonian, Yunnan Province, China

doi:10.1016/0034-6667(95)00120-4

Review of Palaeobotany and Palynology

Volume 93, Issues 1–4, October 1996, Pages 77-88

https://doi.org/10.1016/0034-6667(95)00120-4 Get rights and content

Abstract

Specimens from the Lower Devonian (possibly Pragian) Posongchong Formation of Wenshan, southeastern Yunnan Province, China, originally described as Zosterophyllum contiguum Li et Cai are reinterpreted and placed in the new combination Demersatheca contigua Li et Edwards, comb. nov. They consist of strobili in which sporangia, inserted decussately, form four vertical rows. The sporangia themselves have two valves, splitting around the convex margin, and are sunk into the strobilar axis such that only the abaxial valves, circular to elliptical in outline, are visible. Their contours are continuous with the surface of the strobilus producing a cylindrical structure. The strobili morphologically most closely resemble those of Zosterophyllum, but more detailed comparison is impossible because of the absence of anatomical information on the Chinese specimens.

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Cited by (17)

Morphology, nomenclature and potential paleophytogeographic implication of Demersatheca contigua (Zosterophyllopsida) from the Lower Devonian of Yunnan and Guangxi, southwestern China
2020, Review of Palaeobotany and Palynology
Citation Excerpt :
Remark: Li and Cai (1977) established Zosterophyllum contiguum based on four specimens (PB6467, PB6468, PB6469 and PB6470) but did not assign a holotype from their collection. Hao (1992) transferred Z. contiguum to Z. australianum based on observations on the new materials from the Posongchong Formation, Li and Edwards (1996) thought that the characters of Li and Cai (1977)’s Z. contiguum did not conform to those of the genus Zosterophyllum and transferred the plant to a new combination of Demersatheca contigua. They also assigned the specimen PB6467 from Li and Cai (1977)’s original collection as the holotype and the specimens CBYn 9004012a, b as the paratype from (Li and Edwards, 1996) their collection.
The early land plant group Zosterophyllopsida has a wide distribution in the global Silurian to Devonian floras and the morphological study of this group is fundamentally significant to plant evolution. Demersatheca contigua is an endemic zosterophyllopsid of the Early Devonian flora in South China. Here its morphology is studied based on re-examination of the specimens previously attributed to Zosterophyllum contiguum and Z. australianum from the Posongchong Formation of Yunnan and the observations on newly collected specimens from the Cangwu Formation of Guangxi Zhuang Autonomous Region, southwest China. The strobilus of D. contigua consists of four rows of lateral sporangia decussately arranged biconvex sporangia with marginal dehiscence bending towards the strobilus axis to make the strobilus a cylindrical-shape. 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. Demersatheca contigua is a shared plant member of Yunnan and Guangxi Early Devonian flora of southern China and its paleophytogeographic implication to southern China Early Devonian is discussed.
A further study of Zosterophyllum sinense Li and Cai (Zosterophyllopsida) based on the type and the new specimens from the Lower Devonian of Guangxi, southwestern China
2018, Review of Palaeobotany and Palynology
Zosterophyllum sinense Li and Cai was reported in 1977 from the Lower Devonian Cangwu Formation, eastern Guangxi of China but was rarely acknowledged by authors for its obscure original description. Based on the re-observations to the type specimens and newly-collected specimens of Z. sinense, its detailed morphological information is revealed. Zosterophyllum sinense consists of tufted rooting system and axes, sporangia with long and straight stalks and two unequal valves, are helically and loosely arranged forming the terminal spikes. By far Z. sinense is only reported from the Lower Devonian of Guangxi, palaeogeographically belonging to the Cathaysia Block, a sub-region of the whole South China Block. An Early Devonian floristic distinction is suggested by the plant components between the Yangtze and Cathaysia blocks.
Silurian-Devonian terrestrial revolution in South China: Taxonomy, diversity, and character evolution of vascular plants in a paleogeographically isolated, low-latitude region
2018, Earth-Science Reviews
The radiation of vascular plants during the mid to late Paleozoic has been considered one of the most important drivers of change in Earth's terrestrial environments. Non-marine deposits of the South China Block document plant diversification through the crucial Silurian and Devonian periods in a series of well-preserved fossil assemblages when this block occupied a paleoequatorial to low-latitude position and was isolated from the Laurussia paleocontinent. Significant plant fossils include the Pridoli and Early Devonian assemblages, from Yunnan and Sichuan provinces, southwestern China, and the Pragian Posongchong Flora from the Posongchong Formation of Wenshan, Yunnan. The Middle Devonian (Givetian) Haikou Formation and correlative strata supported diverse lycopsids and euphyllophytes, documenting landscapes with the first tree-like plants in South China. The Late Devonian Huangjiadeng, Xiejingsi and Wutong formations, particular the latter, preserve an abundance of lycopsids, fern-like plants, sphenopsids and seed plants, revealing complex plant communities. The taxonomic diversity in South China is characterized by a gradual increase from the Pridoli, with great diversification during the Pragian, a gap in the Emsian-Eifelian record, and a moderate increase in the Givetian and Frasnian, followed by a 2–3 times increase in the Famennian. Although the raw diversity pattern is somewhat obscured by different sampling intensity, the apparent increases during the Pragian and Famennian seem to be bona fide radiation events. Phytogeographically, the endemism of Early and Middle Devonian floras of South China has been supported by increasing paleobotanical data. The Late Devonian floras of South China began to share some, primarily arborescent species with other parts of the world. Axial diameter, leaf size, and multiple-character-based morphological disparity (mean pairwise dissimilarity) show stepwise evolutionary increase through the Devonian in parallel with the rise of taxonomic diversity. New integrative studies will further illuminate the terrestrialization process and the environmental impact of vascular plants.
Additional observations on Zosterophyllum yunnanicum Hsü from the Lower Devonian of Yunnan, China
2015, Review of Palaeobotany and Palynology
Investigation of unfigured specimens in the original collection of Zosterophyllum yunnanicum Hsü, 1966 from the Lower Devonian (upper Pragian to basal Emsian) Xujiachong Formation, Qujing District, Yunnan, China has provided further data on both sporangial and stem anatomy. We show that the sporangia dehisced into more or less equal valves through a mechanism that involved the development of large thick-walled cells. Furthermore the coalified xylem is composed of tracheids with G-type thickenings (predominantly annular secondary thickenings with small circular to irregular perforations in the intervening wall), confirming the presence of this form of vascular element in the genus Zosterophyllum. The species diagnosis is emended. Characterisation of dehiscence mechanisms in fossil sporangia is complicated by their different modes of preservation. A brief critical survey of the marginal features in bivalved sporangia in zosterophylls and other selected species is followed by a discussion on their putative functional significance. Preservation notwithstanding, we identify clear differences in mechanisms related to the nature of the underlying cellular structure of the dehiscence feature. The distinctive groove present in many species might represent a mechanism for regulating the timing of dehiscence in response to atmospheric conditions.
What is the best way to measure extinction? A reflection from the palaeobotanical record
2013, Earth-Science Reviews
Documenting extinction phenomena remains a vital topic in palaeontology, especially in the context of the marine fossil record. It has been widely assumed that the methods that have been developed in these studies are of universal application throughout palaeontology, but there have been few attempts to test them with plant fossils. We explored the adequacy of the most common methods for documenting extinction events and the associated loss of diversity through time by exploring the monographic knowledge of tracheophytes, especially the record of non-flowering seed-plants. The measure of extinctions was addressed by evaluating diversity fluctuations and the corresponding sampling biases, by measuring levels of taxonomic extinctions, and by exploring disruptions to similarity patterns between time units. Results revealed a strong relationship between diversity and sampling effort based on various different sampling proxies. This suggests that it is vital to take into account the effect of sampling bias when trying to use palaeobotanical diversity dynamics to quantify the real scale of extinction. After testing 16 metrics in two different temporal frameworks, by using criteria like the adjustment between the descriptive extinction metric and the derived probabilistic profile, the interpretation of extinction intensity was overall improved by using normalized metrics that discounted short-lived taxa. Results also revealed that sample size has a significant effect on such analyses and must be evaluated independently for each study before data interpretation. Complementarily, the results showed how the main disturbances of diversity curves generally attributed to extinction events are reflected as abrupt reductions of similarity coefficients between successive time units, which are clearly revealed using clustering methods.
Riccardiothallus devonicus gen. et sp. nov., the earliest simple thalloid liverwort from the Lower Devonian of Yunnan, China
2012, Review of Palaeobotany and Palynology
This paper describes a fossil liverwort in the Posongchong Formation, Lower Devonian (Pragian), Yunnan, China preserved as a partially permineralized compression in gray arenaceous mudstone. The plant comprises a regularly-bifurcating flat ecostate multilayered thallus with entire margins. Following comparisons of this fossil with gametophytes of extant and fossil liverworts, a new genus Riccardiothallus was established in the family Aneuraceae (Jungermanniopsida). The fossil, which appears to be closely similar to several members of the extant genus Riccardia, is the earliest unequivocal megafossil evidence of a liverwort. Considering the sedimentary environment of Riccardiothallus devonicus and the habitats of many extant Riccardia species, we conclude that Riccardiothallus devonicus probably lived in a warm and humid riverine environment. The age (Pragian, 407–411 Ma) of Riccardiothallus devonicus suggests that the differentiation of Jungermanniopsida and Metzgeriidae was in the Early Devonian, significantly earlier than the assumptions derived from analyses of chloroplast DNA sequences of modern liverworts and current total evidence phylogenies (Late Devonian, 359–385 Ma; Late Carboniferous, 299–307 Ma).

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Review of Palaeobotany and Palynology

Abstract

References (22)

Reclassification of Psilophyta

Taxon

Morphology of Vascular plants

On plant remains from the Silurian of Victoria, Australia, that extend and connect floras hitherto described

Philos. Trans. R. Soc.

Stachyophyton gen. nov. from Lower Devonian and its significance

Acta Bot. Sin.

Huia recurvata—a new plant from Lower Devonian of southeastern Yunnan, China

Acta Bot. Sin.

Phylogenetic relationships of the zosterophylls and lycopsids: evidence from morphology, paleoecology, and cladistic methods of inference

Ann. Mo. Bot. Gard.

Further observations on Zosterophyllum yunnanicum Hsü

Acta Bot. Sin.

A new Lower Devonian genus from Yunnan, with notes on the origin of leaf

Acta Bot. Sin.

Gumuia zyzzata—a new plant from the Lower Devonian of Yunnan

Acta Bot. Sin.

A new zosterophyll from the Lower Devonian (Siegenian) of Yunnan, China

Rev. Palaeobot. Palynol.

Some observations on Zosterophyllum australianum Lang and Cookson from the Lower Devonian of Yunnan, China

Bot. J. Linn. Soc.

Cited by (17)

Morphology, nomenclature and potential paleophytogeographic implication of Demersatheca contigua (Zosterophyllopsida) from the Lower Devonian of Yunnan and Guangxi, southwestern China

A further study of Zosterophyllum sinense Li and Cai (Zosterophyllopsida) based on the type and the new specimens from the Lower Devonian of Guangxi, southwestern China

Silurian-Devonian terrestrial revolution in South China: Taxonomy, diversity, and character evolution of vascular plants in a paleogeographically isolated, low-latitude region

Additional observations on Zosterophyllum yunnanicum Hsü from the Lower Devonian of Yunnan, China

What is the best way to measure extinction? A reflection from the palaeobotanical record

Riccardiothallus devonicus gen. et sp. nov., the earliest simple thalloid liverwort from the Lower Devonian of Yunnan, China