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Zosterophyllum spathulatum Li and Cai from the Lower Devonian of Yunnan Province, China, is Adoketophyton subverticillatum (Li and Cai) Li and Edwards, 1992, with a discussion of spatial–temporal distribution of Adoketophyton

Published online by Cambridge University Press:  22 July 2025

Pu Huang Open the ORCID record for Pu Huang [Opens in a new window]  and
Hourui Zhang
Pu Huang*
Affiliation:
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
Hourui Zhang
Affiliation:
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
*
Corresponding author: Pu Huang; Email: puhuang@nigpas.ac.cn
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Abstract

The late Silurian to Early Devonian floras in the South China Block provide important evidence for the radiation of early land plants, including the well-known Posongchong Formation and Xujiachong Formation of Yunnan Province and the Pingyipu Group of Sichuan Province. However, some taxa in these stratigraphic units are described on the basis of limited specimens, or even a single and/or poorly preserved specimen, and need further investigation. The re-investigation of specimen PB6458 from the Xujiachong Formation at the Xujiachong section near Xujiachong Village, Qujing City, Yunnan Province, which is the holotype of Zosterophyllum spathulatum Li and Cai, 1977, reveals some new characters of its strobilus, sporophylls, and sporangia and denies its assignment to Zosterophyllum Penhallow, 1892. Instead, this specimen should be assigned to Adoketophyton subverticillatum (Li and Cai) Li and Edwards, 1992. This taxonomic revision extends the paleogeographic distribution of Adoketophyton Li and Edwards, 1992 and further enhances this genus as one of the index fossils of Lower Devonian non-marine strata in the South China Block.

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Journal of Paleontology , Volume 99 , Issue 2 , March 2025 , pp. 275 - 282
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© The Author(s), 2025. Published by Cambridge University Press on behalf of Paleontological Society

Non-technical Summary

The fossil record from the South China Block provides important evidence for the radiation of early land plants during the late Silurian to Early Devonian. However, some taxa described in the earlier studies need further investigation. In this article, we examine specimen PB6458, originally described as the holotype of Zosterophyllum spathulatum, and revise it to Adoketophyton subverticillatum. Adoketophyton shows a strobilus with several fertile units, each of which comprises a sporangium enclosed in a single fan-shaped sporophyll. Our new taxonomic revision extends the paleogeographic distribution of Adoketophyton in South China.

Introduction

The radiation of early land plants during the late Silurian to Early Devonian is a key event in the evolutionary history of life on Earth (Knoll et al., Reference Knoll, Niklas, Gensel and Tiffney1984; Kenrick and Crane, Reference Kenrick and Crane1997; Hao and Xue, Reference Hao and Xue2013), and this event has been demonstrated in numerous floras around the world, such as those from Laurussia, Gondwana, and South China Block (Xue et al., Reference Xue, Huang, Wang, Xiong, Liu and Basinger2018; Gess and Prestianni, Reference Gess and Prestianni2021; Capel et al., Reference Capel, Cleal, Xue, Monnet, Servais and Cascales-Miñana2022). Since accurate taxonomy is the fundamental basis of biodiversity estimation, our understanding of diversity patterns will be deepened along with the advances in taxonomy. Raymond et al. (Reference Raymond, Parker, Barrett and Tiffney1985) identified three major phytogeographic units during the middle Pragian to Emsian (Early Devonian): Southern Gondwanan, Australian, and equatorial–middle latitude unit consisting of Siberia, North America, Europe, Kazakhstan, and China. Later, as knowledge about early land plants in China accumulated, the South China Block has been regarded as an individual phytogeographic unit distinct from Laurussia (Edwards and Berry Reference Edwards, Berry and Cleal1991; Edwards et al., Reference Edwards, Li and Berry2022).

Re-investigations of previous work based on taxonomic advances on early land plants provide a better understanding of the Early Devonian floras in South China. Pioneering papers by Halle (Reference Halle1927, Reference Halle1936) described “Arthrostigma gracile Dawson” (= Drepanophycus spinaeformis Göppert, Reference Göppert1852) from the Lower Devonian of Qujing, Yunnan, on the basis of a collection made by V.K. Ting and Y.L. Wang. Some fragmentary specimens of cf. Zosterophyllum and Z. yunnanicum Hsü, Reference Hsü1966 were later reported from Qujing (Hsü, Reference Hsü1946, Reference Hsü1966). Numerous specimens from the Lower Devonian of southwestern China were described by Li and Cai (Reference Li and Cai1977, Reference Li and Cai1978), including at least 29 species of Zosterophyllum (including seven new species) and other new plants. Most of these Zosterophyllum species have been re-investigated, resulting in adjustment at the species level or recognition of new genera (Table 1). However, some species remain for further examination including, Z. spathulatum Li and Cai, Reference Li and Cai1977 and Z. bifurcatum Li and Cai, Reference Li and Cai1977 (Edwards et al., Reference Edwards, Yang, Hueber and Li2015).

Table 1.

Selected plant taxa reported from the Lower Devonian of the South China Block in earlier works and their later revisions. Note: †, from Halle (Reference Halle1936); ※, from Hsü (Reference Hsü1966); #, from Li and Cai (Reference Li and Cai1977); § from Li and Cai (Reference Li and Cai1978); in addition, there are many species with open nomenclature, and their specimens are too poorly preserved and thus not considered here

Recently, we carefully re-investigated the collection of Li and Cai (Reference Li and Cai1977, Reference Li and Cai1978), which is housed at Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (NIGPAS). Within this collection, specimen PB6458 was assigned by Li and Cai (Reference Li and Cai1977) as the holotype of their new species, Zosterophyllum spathulatum. We now know that it belongs to Adoketophyton subverticillatum (Li and Cai) Li and Edwards, Reference Li and Edwards1992 in light of the new characters revealed by dégagement. In this article, we provide a detailed description of specimen PB6458 and perform a taxonomic revision. Then we address the spatial–temporal distribution of Adoketophyton Li and Edwards, Reference Li and Edwards1992 in the South China Block.

Material and methods

Specimen PB6458 was collected from the upper part of the Xujiachong Formation at the Xujiachong section near Xujiachong Village, Qujing City, Yunnan Province (Figs. 1, 2; Li and Cai, Reference Li and Cai1977, Reference Li and Cai1978; Wang et al., Reference Wang, Hao and Liu2002). The specimen was first described by Li and Cai (Reference Li and Cai1977) under the new species Zosterophyllum spathulatum, associated with the macrofossil plant “Drepanophycus spinaeformis” and the spores Apiculiretusispora plicata (Allen) Streel, Reference Streel1967, Retusotriletes simplex Naumova, Reference Naumova1953, and R. reculitus Lu and Ouyang, Reference Lu and Ouyang1976, as well as some fragments of fish (Li and Cai, Reference Li and Cai1978; Fig. 2). This specimen is preserved as an impression on a yellow siltstone matrix.

Figure 1.

Geological map showing the fossil locality (the Xujiachong section) near Xujiachong Village, Qujing, Yunnan Province, southwestern China (modified from Hao and Xue, Reference Hao and Xue2013).

Figure 2.

Lithological column and fossil content of the Xujiachong Formation at the Xujiachong section. The stratigraphic division is based on the original description by Li and Cai (Reference Li and Cai1978) and later modification by Wang et al. (Reference Wang, Hao and Liu2002).

The Xujiachong Formation (or “Longhuashan Formation” in Li and Cai, Reference Li and Cai1978) contains more than 90 sedimentary cycles, and each cycle is roughly composed of red mudstone and gray-green siltstone intercalated with conglomerate, thickly bedded sandstone, or thinly bedded sandstone (Fig. 2; Li and Cai, Reference Li and Cai1977, Reference Li and Cai1978; Cai, Reference Cai2000; Wang et al., Reference Wang, Hao and Liu2002; Liu et al., Reference Liu, Hao, Wang and Liu2004; Wellman et al., Reference Wellman, Zhu, Marshall, Wang, Berry and Xu2012; Xue et al., Reference Xue, Deng, Huang, Huang and Benton2016). This formation is rich in macrofossil plants, bearing Bracteophyton variatum Wang and Hao, Reference Wang and Hao2004, Drepanophycus qujingensis, Guangnania cuneata Wang and Hao, Reference Wang and Hao2002, Hedeia sinica Hao and Gensel, Reference Hao and Gensel1998 (or Yarravia sinica (Hao and Gensel) McSweeney et al., Reference McSweeney, Shimeta and Buckeridge2021 based on the recent systematic treatment sensu McSweeney et al. (Reference McSweeney, Shimeta and Buckeridge2021), Hsüa deflexa Wang et al., 2003 (Wang et al., Reference Wang, Hao and Wang2003a), Hsüa robusta Li, Reference Li1982, Huia gracilis Wang and Hao, Reference Wang and Hao2001, Zosterophyllum yunnanicum, Z. australianum Lang and Cookson, Reference Lang and Cookson1930, and Z. bifurcatum (Fig. 2; Hsü, Reference Hsü1966; Li and Cai, Reference Li and Cai1977; Li, Reference Li1982; Li and Edwards, Reference Li and Edwards1995; Hao and Gensel, Reference Hao and Gensel1998; Wang and Hao, Reference Wang and Hao2001, Reference Wang, Hao and Liu2002, Reference Wang and Hao2004; Wang et al., Reference Wang, Hao and Wang2003a, Reference Wang, Hao and Wangb). The upper part of this formation was considered to be Pragian to ?earliest Emsian in age according to comprehensive analyses of spore assemblages (Wellman et al., Reference Wellman, Zhu, Marshall, Wang, Berry and Xu2012). However, considering the absence of other biostratigraphically useful co-occurring fossils, the correlation between spore assemblages of Laurussia and South China needs further investigation (Edwards et al., Reference Edwards, Yang, Hueber and Li2015).

The gross morphology of the strobilus and detailed fertile units of specimen PB6458 were photographed under stereomicroscope Axio Zoom V16, and the line drawings were drawn by the software CorelDRAW. Measurements of axis and fertile units were made using software ImageJ 1.44 (http://rsb/info.nih.gov/ij/index.html).

Repository and institutional abbreviation

Specimen PB6458 is deposited in Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (NIGPAS), China.

Systematic paleobotany

Class, order, and family incertae sedis

Genus Adoketophyton Li and Edwards, Reference Li and Edwards1992

Type species

Adoketophyton subverticillatum (Li and Cai) Li and Edwards, Reference Li and Edwards1992, from the Posongchong Formation at Wenshan, Yunnan Province, China.

Diagnosis

See Li and Edwards (Reference Li and Edwards1992, p. 259).

Adoketophyton subverticillatum (Li and Cai) Li and Edwards, Reference Li and Edwards1992

Figure 3

Figure 3.

Adoketophyton subverticillatum (Li and Cai) Li and Edwards, Reference Li and Edwards1992 from the Xujiachong Formation of the Xujiachong section. Specimen PB6458, holotype of Zosterophyllum spathulatum Li and Cai, Reference Li and Cai1977. (1) Strobilus. Arrows c–f point to the parts enlarged in (3–6), respectively. (2) The interpretive line drawing of the strobilus in (1) showing strobilar axis (Ax) and 14 fertile units (numerals 1–14), which consist of sporophylls (L) and sporangia (S) inside; sporophylls 6 and 14 are attached to the strobilar axis, as shown by a gradient color. (3) A fan-shaped sporophyll with a stalk (St). (4) A curved sporophyll (L) and a sporangium (S), showing the dehiscence line (arrow) along the distal margin. (5) A sporangium (S) consisting of two valves (V) covered by a sporophyll (L). (6, 7) Serial dégagement stages of a fertile unit composed of a fan-shaped sporophyll (L) and a sporangium (S). (8) Enlargement of the elliptical sporangium in (7) showing that valve wall extends continuously along the thickened border (arrows). (1, 2) Scale bars = 5 mm; (3, 6, 7) scale bars = 2 mm; (4, 5, 8) scale bars = 1 mm.

Reference Li and Cai1977     Zosterophyllum subverticillatum; Li and Cai, p. 24, pl.3, figs. 1–3, 3a.

Reference Li and Cai1977   Zosterophyllum spathulatum; Li and Cai, p. 17, pl.2, figs. 16, 16a.

Reference Li and Edwards1992      Adoketophyton subverticillatum; Li and Edwards, p. 259, pls. 1–4.

Reference Hao, Wang and Beck2003     Adoketophyton subverticillatum; Hao et al., p. 180, pls. 1–3.

Reference Hao and Xue2013     Adoketophyton subverticillatum; Hao and Xue, p. 140, figs. 4.44–4.46.

Reference Huang, Wang and Zhang2022a   Adoketophyton subverticillatum; Huang et al., p. 400, fig. 4.

Holotype

Specimen PB6465 in Li and Cai (Reference Li and Cai1977, pl. 3, fig. 2), from the Posongchong Formation at Wenshan, Yunnan Province, China.

Occurrence

Specimen PB6458, from the Lower Devonian Xujiachong Formation, near Xujiachong Village, Qujing City, Yunnan Province. Other occurrences include the Lower Devonian Posongchong Formation at Wenshan and Mengzi, Yunnan Province, and the Lower Devonian Mangshan Group at Baoyang, Duyun, Guizhou Province.

Description

The morphological terms involving fertile structures in this paper mainly follow those of Hao et al. (Reference Hao, Wang and Beck2003) and Hao and Xue (Reference Hao and Xue2013): fertile units, strobilar axis, sporangium, sporophyll (= bract-like flattened appendage in Li and Edwards, Reference Li and Edwards1992) and stalk of sporophyll.

The specimen PB6458 shows an incomplete strobilus, with at least 14 fertile units, and both ends of the strobilus are broken (Fig. 3.1, 3.2). The strobilus is 32.5 mm long and 7.4 mm wide, and the strobilar axis is ~0.9 mm wide (Fig. 3.1). In this specimen, fertile units 1 and 2 appear to be oppositely arranged on the strobilar axis (at the two opposite sides of the axis), and at an upper level, fertile unit 3 is attached on the strobilar axis at a position between fertile units 1 and 2. For fertile units 12 and 13, the tops of their sporophylls reach the same level, and fertile unit 14 extends from the axis from a position between fertile units 12 and 13. Thus the fertile units seem to be oppositely and decussately inserted. Two fertile units are well preserved (Fig. 3.2, fertile units 6 and 14; Fig. 3.3, 3.6), which comprise fan-shaped sporophylls and elliptical sporangia enclosed in sporophylls (Fig. 3.6–3.8).

The fan-shaped sporophylls are 7.9–8.2 mm high and 4.8–5.8 mm at the widest part (Fig. 3.3–3.6). The stalks of sporophylls are 0.8–0.9 mm wide and 3.2–3.4 mm long; they gradually widen and connect with the broad sporophyll lamina (Fig. 3.3, arrow St). In lateral view, the sporophyll lamina shows a convex inner side and concave outer side (Fig. 3.4) and obviously exceeds the length of the sporangium (Fig. 3.4–3.7). A complete sporangium, recognized by serial dégagement, is elliptical in outline, ~3.4 mm wide and 2.4 mm high (Fig. 3.6–3.8). A thickened border extends along the distal margin of sporangia, ~0.3 mm wide, and the dehiscence divides each sporangium into two valves (Fig. 3.4, 3.5).

Material

Specimen PB6458 housed at Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences.

Remarks

The newly recognized sporophyll–sporangium units in specimen PB6458 are distinct from the members of Zosterophyllum, which lack appendages accompanying their sporangia (Penhallow, Reference Penhallow1892; Li and Edwards, Reference Li and Edwards1992). Each fertile unit of specimen PB6458 is formed by a single fan-shaped sporophyll and a sporangium, the defining character of the genus Adoketophyton.

Three species of Adoketophyton—A. subverticillatum, A. parvulum Zhu et al., Reference Zhu, Xue, Hao and Wang2011, A. pingyipuensis Edwards and Li, Reference Edwards and Li2018—have been reported from the Lower Devonian of South China, along with some fragmentary strobili assigned to Adoketophyton sp. These species are different in strobilar axis width, arrangement of fertile units, shape of sporophylls, and relative sizes of sporangia (Table 2). The sizes of sporophylls and sporangia of specimen PB6458 are comparable to those of A. subverticillatum (Table 2). The sporangial height is ~1/2 to 2/3 the height of sporophylls in specimen PB6458, different from A. parvulum. The typical fan-shaped sporophylls in specimen PB6458 are distinct from the narrow fan-shaped sporophylls of A. pingyipuensis from the Pingyipu Group and Adoketophyton sp. from the Posongchong Formation. Hence, specimen PB6458 clearly belongs to A. subverticillatum.

Table 2.

Morphological comparisons of species of Adoketophyton Li and Edwards, Reference Li and Edwards1992 from the South China Block (units in mm)

Discussion

Taxonomy and spatial–temporal distribution of Adoketophyton

Adoketophyton is widely distributed in the South China Block, including Yunnan, Sichuan, and Guizhou areas (Fig. 4; Hao and Xue, Reference Hao and Xue2013; Edwards and Li, Reference Edwards and Li2018; Huang et al., Reference Huang, Wang and Zhang2022a). Its previous records include those from the Posongchong Formation (b, c in Fig. 4), Mangshan (d in Fig. 4), and Pingyipu (e in Fig. 4) groups. Adoketophyton in the Posongchong Formation of Yunnan Province contains A. subverticillatum, A. parvulum, and one undetermined species. The new find of Adoketophyton in this study extends its paleogeographic distribution and stratigraphic occurrence, now also in the Xujiachong Formation (a in Fig. 4). Adoketophyton represents another widespread genus in the Lower Devonian of the South China Block, alongside Zosterophyllum.

Figure 4.

Localities of Adoketophyton in the South China Block around the Early Devonian South China Sea (modified from Xue et al., Reference Xue, Huang, Wang, Xiong, Liu and Basinger2018, their fig. 4A). Fm. = Formation; Gp. = Group.

In the Posongchong Formation, Adoketophyton subverticillatum occurs at four outcrops in Wenshan and Mengzi, Yunnan Province, according to the summary in Hao and Xue (Reference Hao and Xue2013), while in the Mangshan Group and the Xujiachong Formation, the discovered specimens are rare, and further work is needed. The differentiation of taxonomic components between the Posongchong Formation and Xujiachong Formation is interpreted mainly as a result of different sedimentary environments (Wang et al., Reference Wang, Hao and Liu2002; Liu et al., Reference Liu, Hao, Wang and Liu2004). The Posongchong Formation is interpreted as representing near-channel overbank to lowland backswamp floodplain environments close to shoreline, while the Xujiachong Formation probably represents fluvial deposits on the presumed delta plain under a seasonally wet–dry climate (Liu et al., Reference Liu, Hao, Wang and Liu2004; Hao and Xue, Reference Hao and Xue2013; Xue et al., Reference Xue, Deng, Huang, Huang and Benton2016). The new record of A. subverticillatum in the Xujiachong Formation, as well as the same species from the Mangshan Group of Guizhou Province (Huang et al., Reference Huang, Wang and Zhang2022a), indicate that this plant might have adapted to wider habitats and more diverse environments.

Stratigraphic significance of Adoketophyton

Li and Cai (Reference Li and Cai1978, Reference Li and Cai1979) divided the Early Devonian plants in the South China Block into three plant assemblages, Uncatoella verticillata Li and Cai, Reference Li and Cai1978–Zosterophyllum sp., Z. myretonianum–Z. australianum, and Drepanophycus spinaeformis–Z. yunnanicum from early to late Early Devonian. Cai and Wang (Reference Cai, Wang and Li1995) suggested the Z. yunnanicum assemblage to replace the Drepanophycus spinaeformis–Z. yunnanicum assemblage in light of the wide distribution of Drepanophycus in the whole Devonian. However, some taxa have been revised, such as Z. myretonianum Penhallow, Reference Penhallow1892 and D. spinaeformis (Li and Edwards, Reference Li and Edwards1995; Edwards et al., Reference Edwards, Geng and Li2016; Table 1). Recently, Qie et al. (Reference Qie, Ma, Xu, Qiao, Liang, Guo, Song, Chen and Lu2019) established the Zosterophyllum–Xitunia assemblage (Lochkovian), Zosterophyllum–Yunia assemblage (Pragian), and Psilophyton–Hsüa assemblage (Emsian) in the South China Block. However, these assemblages still need further investigation, including temporal and spatial ranges of some taxa as well as their nature.

Adoketophyton subverticillatum of the Posongchong Formation is Pragian in age based on spore assemblages (Hao and Xue, Reference Hao and Xue2013; Cascales-Miñana et al., Reference Cascales-Miñana, Xue, Rial, Gerrienne, Huang and Steemans2019). The age of A. subverticillatum in the upper part of the Xujiachong Formation is tentatively assignable to Pragian to ?earliest Emsian, but cautions should be made for the exact age of this formation (Edwards et al., Reference Edwards, Yang, Hueber and Li2015). The age of the Mangshan Group is considered Pragian from floral comparisons with the Xujiachong Formation and Posongchong Formation (Huang et al., Reference Huang, Wang and Zhang2022a, Reference Huang, Liu and Xueb; Zhou et al., Reference Zhou, Zhao, Wang, Wu, Xiao and Huang2022). A. parvulum and Adoketophyton sp. occur only in the Pragian-aged Posongchong Formation (Zhu et al., Reference Zhu, Xue, Hao and Wang2011; Hao and Xue, Reference Hao and Xue2013), while A. pingyipuensis is probably the earliest record of this genus, being Lochkovian/early Pragian in age (Edwards and Li, Reference Edwards and Li2018). To summarize, the species of Adoketophyton, mostly found within the Pragian-age deposits, can be considered one of the index fossils of Lower Devonian non-marine strata in the South China Block.

Conclusion

Specimen PB6458 originally described as the holotype of Zosterophyllum spathulatum from the Xujiachong Formation, Qujing, Yunnan Province, is revised as Adoketophyton subverticillatum on the basis of the new characters revealed by serial dégagement. This taxonomic revision adds a new record of Adoketophyton. The genus Adoketophyton can be considered one of the index fossils for the correlation of non-marine Lower Devonian strata in the South China Block.

Acknowledgments

We thank J. Xue of Peking University for helpful discussions and C. Chu of NIGPAS for the loan of specimens. We also thank C. Berry, an anonymous reviewer, and associate editor W. DiMichele for their very helpful suggestions. This work was supported by the National Natural Science Foundation of China (numbers 42472028, 41802003).

Competing interests

The authors declare none.

Footnotes

Handling Editor: William DiMichele

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Figure 0

Table 1. Selected plant taxa reported from the Lower Devonian of the South China Block in earlier works and their later revisions. Note: †, from Halle (1936); ※, from Hsü (1966); #, from Li and Cai (1977); § from Li and Cai (1978); in addition, there are many species with open nomenclature, and their specimens are too poorly preserved and thus not considered here

Figure 1

Figure 1. Geological map showing the fossil locality (the Xujiachong section) near Xujiachong Village, Qujing, Yunnan Province, southwestern China (modified from Hao and Xue, 2013).

Figure 2

Figure 2. Lithological column and fossil content of the Xujiachong Formation at the Xujiachong section. The stratigraphic division is based on the original description by Li and Cai (1978) and later modification by Wang et al. (2002).

Figure 3

Figure 3. Adoketophyton subverticillatum (Li and Cai) Li and Edwards, 1992 from the Xujiachong Formation of the Xujiachong section. Specimen PB6458, holotype of Zosterophyllum spathulatum Li and Cai, 1977. (1) Strobilus. Arrows c–f point to the parts enlarged in (3–6), respectively. (2) The interpretive line drawing of the strobilus in (1) showing strobilar axis (Ax) and 14 fertile units (numerals 1–14), which consist of sporophylls (L) and sporangia (S) inside; sporophylls 6 and 14 are attached to the strobilar axis, as shown by a gradient color. (3) A fan-shaped sporophyll with a stalk (St). (4) A curved sporophyll (L) and a sporangium (S), showing the dehiscence line (arrow) along the distal margin. (5) A sporangium (S) consisting of two valves (V) covered by a sporophyll (L). (6, 7) Serial dégagement stages of a fertile unit composed of a fan-shaped sporophyll (L) and a sporangium (S). (8) Enlargement of the elliptical sporangium in (7) showing that valve wall extends continuously along the thickened border (arrows). (1, 2) Scale bars = 5 mm; (3, 6, 7) scale bars = 2 mm; (4, 5, 8) scale bars = 1 mm.

Figure 4

Table 2. Morphological comparisons of species of Adoketophyton Li and Edwards, 1992 from the South China Block (units in mm)

Figure 5

Figure 4. Localities of Adoketophyton in the South China Block around the Early Devonian South China Sea (modified from Xue et al., 2018, their fig. 4A). Fm. = Formation; Gp. = Group.