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Xu, H. Barsassia (Lycopsida). Encyclopedia. Available online: https://encyclopedia.pub/entry/17092 (accessed on 13 June 2024).
Xu H. Barsassia (Lycopsida). Encyclopedia. Available at: https://encyclopedia.pub/entry/17092. Accessed June 13, 2024.
Xu, Hong-He. "Barsassia (Lycopsida)" Encyclopedia, https://encyclopedia.pub/entry/17092 (accessed June 13, 2024).
Xu, H. (2021, December 14). Barsassia (Lycopsida). In Encyclopedia. https://encyclopedia.pub/entry/17092
Xu, Hong-He. "Barsassia (Lycopsida)." Encyclopedia. Web. 14 December, 2021.
Barsassia (Lycopsida)
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Morphology and nomenclature are essential issues of botany, in which both extant and fossil plant taxa follow the same nomenclature code. Devonian (419.2–358.9 Ma) herbaceous lycopsid Barsassia, one of the earliest coal-forming plants in geological history, possesses a characteristic, easily recognized, step-like stem and has been thought to be an index fossil for dating and correlating the Middle Devonian strata, especially those in the paleoblocks of Siberia, Kazakhstan, Xinjiang, and North China. Here, researchers systematically study the Devonian lycopsid Barsassia in terms of its morphology and nomenclature, based on the new materials from the Middle Devonian Hujiersite Formation of West Junggar, Xinjiang, China, and the International Code of Nomenclature for algae, fungi, and plants (Shenzhen Code). Barsassia ornata is determined as the type species of the genus, and a neotype is designated for that name. Barsassia ornata consists of fan- or rectangular-shaped leaves with awl-shaped or finger-like distal tips. Its leaves are pseudo-whorls and imbricately arranged on the stem surface forming distinct step-like structure.

nomenclature Barsassia Devonian paleobotany Xinjiang

1. Introduction

The Devonian Period (419.2–358.9 million years ago) is critical for the origin and the radiation of terrestrial vascular plants. All land plant groups except angiosperm appeared in this period [1], as well as with the rise of the first forest [2][3] that brought profound impacts on Earth’s environment and ecosystem, e.g., a dramatic drop of atmosphere CO2 and the extensive terrestrial weathering [4] caused by plants rooting system development [5][6]. Devonian plant fossil records show a critical and distinctive window for understanding the plant and paleoenvironment evolution [7].
The herbaceous lycopsid Barsassia has been thought to be an important fossil taxon for dating and correlating the Middle Devonian strata, especially those in Siberia, Kazakhstan, Xinjiang, and North China paleoblocks [8][9][10][11][12][13], for its characteristic and easily recognized step-like stem. Much terrestrial organic carbon produced from Devonian Barsassia and other lycopsids was buried and formed the earliest coal seams [14] and potential petroleum reserve, e.g., only 80–100 cm thick carbonaceous beds in the Middle Devonian of Junggar, Xinjiang [12][13][15][16], Kuznetsk Basin, southwestern Siberia [17][18], and Luquan, Yunnan, southern China [14][19].
Barsassia was established by Zalessky in 1933 [17] based on materials from the Middle Devonian of Barsas, Siberia, Russia. There have been four species of Barsassia since then, including the type species Barsassia ornata from the Middle Devonian of Siberia and North Xinjiang [17] characterized by fleshy fan-shaped leaf, Barsassia platyphylla from the Middle Devonian of Siberia, Russia [20]Barsassia sibirica from the Middle Devonian of Junggar, Xinjiang, China [9]Barsassia grandis with rectangular-shaped leaf from the Middle Devonian of Kazakhstan [21], and Barsassia plana with broad fan-shaped leaf from the Middle Devonian of Kazakhstan [21]. However, the morphological characteristics of different species of Barsassia and their nomenclature are controversial, as a result of little attention paid to Central Asian materials and the Russian literature.

2. Systematic Paleobotany

Class: Lycopsida
Order: Drepanophycales
Family: Asteroxylaceae Kidston et Lang, 1920 [22]
Genus: Barsassia (Zalessky, 1933) [17]
Type species: Barsassia ornata (Zalessky, 1933) [17]
Generic diagnosis: Herbaceous lycopsid. Stem bifurcated, surface with step-like structure formed by pseudo-whorls, tightly, and imbricately arranged leaves. Leaf persistent, fan-shaped or rectangular-shaped with a distal leaf tip. Stele star-shaped, tracheid spirally thickened.
Remark: The leafy stem of Barsassia conforms the characters of the Class Lycopsida. Snigirevskaya and Bogdanova (1992) [22] reported its star-shaped stele and assumed its anatomical similarities to Asteroxylon [23][24]. We here follow their classification and assign Barsassia to the Order Drepanophycales and the Family Asteroxylaceae.
Species: Barsassia ornata [17].
Synonyms (this synonym list shows that all illustrated specimens under below-listed names are transferred to Barsassia ornata, although some of these names are identical to ours):
1933 Barsassia ornata, Zalessky, Figures 1 and 2.
1975 Barsassia ornata, Stepanov, Plate XXV, Figures 1–6 and 9.
1975 Barsassia platyphylla, Stepanov, Plate XXV, Figures 7 and 8.
1983 Barsassia sibirica, Dou et al., Plate 201, Figures 3–5, 9, 11 and 12.
1983 Barsassia sibirica, Huang, Plate II, Figures 4–6.
1991 Barsassia grandis, Senkevitsch, Plate LXIV, Figures 1–4.
1991 Barsassia plana, Senkevitsch, Plate LXIV, Figures 5–7.
1992 Barsassia ornata, Snigirevskaya and Bogdanova, Plate III, Figures 1 and 2.
2010 Barsassia ornata, Snigirevskaya, Plates 1, 3–6.
2021 Barsassia sibrica, Liu et al., Figure 3A,B.
Specific diagnosis: Stem at least 161 mm long and 6.6–12 mm wide without counting leaves. Leaves tightly, pseudo-whorls, and imbricately arranged on the stem forming step-like structure, 3–6 leaves per gyre. Leaf with fan- or rectangular-shaped main body and a short awl-shaped to long finger-like distal tip. The distal tip ranges from not visible to up to 1.1 mm long. The whole leaf up to 1.7–4.4 mm in height and 3.3–4.5 mm in width.
Neotype: PB23703 (Figure 1B).
Figure 1. Barsassia ornata [17] from the Middle Devonian Hujiersite Formation, Hoxtolgay, West Junggar, Xinjiang, China. (A) A bifurcated leafy stem with obvious step-like structure on the surface. PB23702. (B) Neotype. Two stems with imbricately and tightly arranged leaves, leaf shape in a variety ranging from fan-shaped (arrow 1), fan-shaped with short awl-shaped tips (arrow 2), and rectangular-shaped (arrow 3) in surface view. Arrow 6 indicates the step-like stem. PB23703. (C,D) A three-dimensional cast of the stem with tipped leaves (arrows), one and its reverse side PB23704. (E) Enlargement of a portion of leafy stem indicated by arrow 2 in A, showing the step-like structure of the stem and dots on leaf surface (arrow).
Horizon and Distribution: The Upper Member of the Hujiersite Formation (Givetian, Middle Devonian), Hoxtolgay, Hoboksar County, West Junggar Basin, Xinjiang Uygur Autonomous Region, China. Fuxingtun Formation (Middle Devonian), Zhangguangcai Mountains, Heilongjiang Province, northeastern China. Barzas Formation (Lower-Middle Devonian), Kuznetsk Basin, southwestern Siberia, Russia. Kazakh Horizon (Middle Devonian), Balkhash Land, Kazakhstan.
Description: The description is based on twenty specimens of our collection, from which 5 pieces are selected and illustrated here. All specimens are leafy stem and conform to the same plant morphology and belong to one plant. No fertile structure is discovered from the whole collection.
From all specimens, leaves are seen to be attached to the stem, indicating that the plant has persistent leaves. The stem is straight or slightly sinuous, at least 161 mm long, and dichotomously branched (Figure 1A), 6.6–12 mm (mean value = 10.3 mm, n = 13) wide without counting laterally attached leaves.
Leaves are tightly imbricate and pseudo-whorls arranged on the stem surface, forming step-like structure with points on the surface (Figure 1 and Figure 2). Three leaves are seen on the single surface in a 10 mm wide stem, indicating that the plant has six leaves per gyre (Figure 1B and Figure 3A). Leaf number per gyre is related to stem width, and in a 6.5 mm wide stem (Figure 1C, D), the number is three. From all specimens of our collection, we see 3–6 leaves per gyre.
Figure 2. Barsassia ornata [17] from the Middle Devonian Hujiersite Formation of the Gannaren Section, West Junggar, Xinjiang, China. (A, B) Part and counterpart specimens showing the leafy stem with step-like structure and rectangular-shaped leaf with lateral tip (arrow). PB23705A, PB23705B. (C) Enlargement of the arrowed portion in B, showing the leaf in lateral view.
Figure 3. Line-drawings of Barsassia ornata [17] leafy stem based on materials from Middle Devonian Hujiersite Formation, West Junggar, Xinjiang, China. (A) From arrow 1 of Figure 1B, showing the fan-shaped leaves in surface view and the arrangement of leaves. (B,C) From Figure 1C,D. Dotted line indicates the leaf margin; the gray disks indicate leaf tips; and leaf tips are numbered and correspond in part and counterpart specimens. (D) From arrow 4 of Figure 1B, showing leaves in lateral view with tips (grey disks). (E). From arrowed portion of Figure 2B, showing the leaf in lateral view with obvious tip (gray disk) and the rectangular-shaped leaf. Black arrows show the leaf margin. The lateral leaf shows rectangular-shaped leaf after unfolding (F).
The leaf is fan- or rectangular-shaped with a distal tip (Figure 1B–D, Figure 3A and Figure 4K–M). The surface of the specimens is undulate seen under microscope, and the leaf margin can be clearly observed (Figure 2 and Figure 3E). The leaf is entirely marginal, 1.7–4 mm (mean value = 2.9 mm, n = 13) in height, i.e., from the base of the leaf to the distal tip, 3.7–4.5 mm (mean value = 4.1 mm, n = 10) wide in its basal portion. The distal tip varies in appearance ranging from short awl-shaped to long finger-like shaped. In some cases, the tip is not visible and occasionally up to 1.1 mm in length. The leaf main body (LM), i.e., the part without counting the tip (Figure 4N), normally has nearly horizontal upper edges. As a result, LM usually shows rectangular shape in surface view (Figure 2 and Figure 3E). The rectangle formed by the LM is clearly edged and slightly fluctuated, and comprises one of the most easily recognized characters of the present plant. The single rectangle is measured as 2.4–4.4 mm (mean value = 3.4 mm, n = 12) in height (Figure 1B, Figure 2 and Figure 3B–F) and 3.3–4.5 mm (mean value = 3.8 mm, n = 7) in width. The leaf in lateral view shows the thick LM with typical upward tip (Figure 1B arrow 4, 5; Figure 1C, D and Figure 2B, C).
Figure 4. Line-drawings of leaf appearances of Barsassia ornata [17] from different localities and a leaf shape diagram. (A) From Figure 1 of [17], under the name of Barsassia ornata from the Middle Devonian of Barzas, southwestern Siberia, Russia. (B) From Figure 2 of [17], under the name of Barsassia ornata from the Middle Devonian of Barzas, southwestern Siberia, Russia. (CD) From Plate XVV. Figure 8 of [20], under the name of Barsassia ornata from the Middle Devonian of Barzas, southwestern Siberia, Russia. (E) From Plate XVV. Figure 2 of [20], under the name of Barsassia platyphylla from the Middle Devonian of Barzas, southwestern Siberia, Russia. (F) From Plate 201. Figure 11 of [9]; under the name of Barsassia sibirica from the Middle Devonian of West Junggar Basin, Xinjiang, China. (G) From Plate 201. Figure 4 of [9], under the name of Barsassia sibirica from the Middle Devonian of West Junggar Basin, Xinjiang China. (H) From Plate LXIV. Figure 2 of [21], under the name of Barsassia grandis from the Middle Devonian of Katbas Mountains, Kazakhstan. (I): From Plate LXIV. Figure 6 of [21], under the name of Barsassia plana from the Middle Devonian of Katbas Mountains, Kazakhstan. (J) From Plate 4 of [25], under the name of Barsassia ornata from the Middle Devonian of southwestern Siberia, Russia. (KM) Based on the Figure 1B of this study, under the name of Barsassia ornata from the Middle Devonian of West Junggar Basin, Xinjiang China. (N) A diagram of leaf shape showing the leaf main body (LM) and tip.

References

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  2. Stein, W.E.; Berry, C.M.; Hernick, L.A.; Mannolini, F. Surprisingly complex community discovered in the mid-Devonian fossil forest at Gilboa. Nature 2012, 483, 78–81.
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  12. Xu, H.H.; Jiang, Q.; Zhang, X.L.; Wang, Y.; Feng, J. On the Mid Devonian Hujiersite flora from West Junggar, Xinjiang, China, its characteristics, age, palaeoenvironment and palaeophytogeographical significances. Acta Palaeontol. Sin. 2015, 54, 230–239, (In Chinese with English summary).
  13. Liu, B.C.; Zong, R.W.; Wang, Y.; Xu, H.H. On the age of Devonian ancient petroleum reservoir in west Junggar, Xinjiang, Northern Xinjiang, China. J. Stratigr. 2021, 45, 196–203, (In Chinese with English summary).
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  22. Snigirevskaya, N.S.; Bogdanova, L.A. Finding of stomata and xylem in plants of the genus Barsassia (Asteroxylaceae, Lycopodiophyta) from the Middle Devonian of the Kuznets basin and some questions of the stomatographic study of ancient plants. Bot. Zhurnal 1992, 77, 58–66.
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