[en] [en] BACKGROUND AND AIMS: Sphenophytes, now restricted to Equisetum, were more diverse during the Paleozoic, particularly within Carboniferous coal swamp ecosystems. Despite their significance, the origins and phylogenetic relationships of sphenophytes with stem-group monilophytes remain poorly understood. In this context, the extinct order Pseudoborniales, typified by Pseudobornia ursina (Nathorst, 1894) from the Late Devonian of Bjørnøya (Norway), plays a key role in understanding the group's origin. However, conflicting interpretations of its reproductive structures have hindered its phylogenetic placement. Here, we provide a new description and reconstruction of the reproductive structures of P. ursina to evaluate its phylogenetic relationships with other sphenophytes and closely-allied groups, as well as to provide an updated perspective on the evolution of key traits among sphenopsids.
METHODS: Fossils from the type locality were re-examined to clarify the morphology of the strobilus and fertile appendages. Comparative analyses were conducted with members of Sphenophyllales, Equisetales, and stem-group monilophytes. Phylogenetic relationships were assessed using parsimony and Bayesian methods.
KEY RESULTS: The strobilus of P. ursina displays distinctive features: (1) stalked, sporangia-bearing appendage, (2) oblique insertion of these structures in the bract axil, (3) ∼30 erect sporangia arranged on a wide-obconical receptacle, and (4) deeply bisected bracts with entire margins and parallel venation. Vegetative characters suggest equisetalean affinities, while reproductive traits more closely resemble stem sphenopsids. This mosaic points to a unique combination of ancestral traits within Sphenopsida, and phylogenetic analyses place P. ursina within Equisetales.
CONCLUSIONS: Our reappraisal of the strobilus of Pseudobornia ursina clarifies both its morphology and its phylogenetic placement, being recovered as part of stem Equisetales, sister to Archaeocalamitaceae. This suggests an evolutionary scenario where fertile appendages of stem sphenophytes became more compact over time, with either a fusion to a bract or the development of fertile internodes, combined to the loss of the bract, leading to the two main clades of Sphenophytes (Sphenophyllales and Equisetales).
TRESVeg - Unveiling the birth of coal forests: Tracing ecosystem resilience and vegetation shifts in deep time
Funders :
French-Speaking Community of Belgium F.R.S.-FNRS - Fonds de la Recherche Scientifique FRIA - Fonds pour la Formation à la Recherche dans l'Industrie et dans l'Agriculture
Supplementary data consist of the following. Appendix S1 - supplementary texts including the list of morphological characters and all scripts for phylogenies. Supplementary tables (Table S1 - Matrix of morphoanatomical characters, Table S2 - First and last appearance datum (FAD-LAD) table, Table S3 - Historical taxonomy at the order level of each discussed species). Supplementary figures (Figure S1 – Strict consensus tree (implied weighting analysis with k = 3), Figure S2 – Strict consensus tree (equal weighting analysis)).
Antevs E, Nathorst AG. 1917. Kohlenfiihrende Kulm auf der Baren Insel. Geologiska Foreningens i Stockholm Forhandlingar 39: 649–653. doi:10.1080/11035891709444424
Arnold CA. 1958. Petrified cones of the genus Calamostachys from the Carboniferous of Illinois. Contributions from the Museum of Paleontology, University of Michigan 14: 149–165.
Banks HP, Leclercq S, Hueber FM. 1975. Anatomy and morphology of Psilophyton dawsonii, sp. n. from the Late Lower Devonian of Quebec (Gaspé), and Ontario, Canada. Palaeontographica Americana 8: 77–125.
Bapst DW. 2012. Paleotree: an R package for paleontological and phylogenetic analyses of evolution. Methods in Ecology and Evolution 3: 803–807. doi:10.1111/j.2041-210X.2012.00223.x
Bateman R. 1991. Palaeobiological and phylogenetic implications of anatomically-preserved Archaeocalamites from the Dinantian of Oxroad Bay and Loch Humphrey Burn, southern Scotland. Palaeontographica Abteilung B 223: 1–59.
Baxter RW. 1972. A comparative study of nodal anatomy in Peltastrobus reedae and Sphenophyllum plurifoliatum. Review of Palaeobotany and Palynology 14: 41–47. doi:10.1016/0034-6667(72)90006-1
Bell MA, Lloyd GT. 2015. Strap: an R package for plotting phylogenies against stratigraphy and assessing their stratigraphic congruence. Palaeontology 58: 379–389. doi:10.1111/pala.12142
Berry CM, Edwards D. 1996. Anapaulia moodyi gen. et sp. nov.: a probable iridopteridalean compression fossil from the Devonian of western Venezuela. Review of Palaeobotany and Palynology 93: 127–145. doi:10.1016/0034-6667(95)00123-9
Berry CM, Stein WE. 2000. A new iridopteridalean from the Devonian of Venezuela. International Journal of Plant Sciences 161: 807–827. doi:10.1086/314295
Berry CM, Stein WE, Cordi J. 2022. A new reconstruction of the Iridopteridalean Ibyka amphikoma Skog et Banks from the middle Devonian of Gilboa, New York State. International Journal of Plant Sciences 183: 450–464. doi:10.1086/720721
Boureau E. 1964. Traité de Paléobotanique. Tome II. Sphenophyta, Noeggerathiophyta. Paris, France: Masson et Cie.
Cariglino B. 2013. Fructification diversity from the La Golondrina Formation (Permian), Santa Cruz Province, Argentina. Geobios 46: 183–193. doi:10.1016/j.geobios.2012.10.017
Chu J, Durieux T, Tomescu AMF. 2024. An early cladoxylopsid with complex vascular architecture: Paracladoxylon kespekianum gen. et sp. nov. from the Lower Devonian (Emsian) of Quebec, Canada. American Journal of Botany 111: e16418. doi:10.1002/ajb2.16418
Cúneo NR, Escapa I. 2006. The equisetalean genus Cruciaetheca nov. from the Lower Permian of Patagonia, Argentina. International Journal of Plant Sciences 167: 167–177. doi:10.1086/497652
Cutbill JL, Challinor A. 1965. Revision of the stratigraphical scheme for the Carboniferous and Permian rocks of Spitsbergen Bjørnøya. Geological Magazine 102: 418–439. doi:10.1017/S0016756800053693
Dallmann WK, Gjelberg JG, Harland WB, et al 1999. Lithostratigraphic lexicon of Svalbard. Review and recommendations for nomenclature use. Upper Palaeozoic to Quaternary bedrock. Norwegian Polar Institute Report 318: 127–214.
D’Antonio MP, Hotton CL, Smith SY, Crane PR, Herrera F. 2024. Reconstruction of an enigmatic Pennsylvanian cone reveals a relationship to Sphenophyllales. American Journal of Botany 111: e16321. doi:10.1002/ajb2.16321
Deng ZZ, Huang P, Liu L, Wang DM, Xue JZ. 2016. New observations of Sphenophyllum pseudotenerrimum Sze (Sphenopsida) from the Late Devonian of South China. Acta Palaeontologica Sinica 55: 45–55.
Durieux T, Lopez MA, Bronson AW, Tomescu AMF. 2021. A new phylogeny of the cladoxylopsid plexus: contribution of an early cladoxylopsid from the Lower Devonian (Emsian) of Quebec. American Journal of Botany 108: 2066–2095. doi:10.1002/ajb2.1752
Elgorriaga A, Escapa IH, Rothwell GW, Tomescu AMF, Rubén Cúneo N. 2018. Origin of Equisetum: evolution of horsetails (Equisetales) within the major euphyllophyte clade Sphenopsida. American Journal of Botany 105: 1286–1303. doi:10.1002/ajb2.1125
Fu Q, Wang Y, Berry CM, Xu HH. 2011. Complex branching patterns in a newly recognized species of Compsocradus Berry et Stein (Iridopteridales) from the Middle Devonian of north Xinjiang, China. International Journal of Plant Sciences 172: 707–724. doi:10.1086/659453
Goloboff PA, Catalano SA. 2016. TNT version 1.5, including a full implementation of phylogenetic morphometrics. Cladistics 32: 221–238. doi:10.1111/cla.12160
Goloboff PA, Torres A, Arias JS. 2018. Weighted parsimony outperforms other methods of phylogenetic inference under models appropriate for morphology. Cladistics 34: 407–437. doi:10.1111/cla.12205
Good CW. 1978. Taxonomic characteristics of Sphenophyllalean cones. American Journal of Botany 65: 86–97. doi:10.1002/j.1537-2197.1978.tb10839.x
Gothan W, Weyland H. 1973. Lehrbuch der Paläobotanik, 3rd edn. Berlin: Walter de Gruyter.
Hoffmeister WS, Staplin FL, Malloy RE. 1955. Mississippian plant spores from the Hardinsburg Formation of Illinois and Kentucky. Journal of Paleontology 29: 372–399.
Huang P, Le L, Lu L, Wang JS, Xue JZ. 2022. Sphenophyllum Brongniart (Sphenopsida) from the Upper Devonian of South China. Palaeoworld 31: 402–418. doi:10.1016/j.palwor.2021.09.007
Huang P, Liu L, Deng Z, Basinger JF, Xue J. 2017. Xihuphyllum, a novel sphenopsid plant with large laminate leaves from the upper Devonian of South China. Palaeogeography, Palaeoclimatology, Palaeoecology 466: 7–20. doi:10.1016/j.palaeo.2016.11.004
Huelsenbeck JP, Ronquist F. 2001. MRBAYES: Bayesian inference of phylogenetic trees. Bioinformatics 17: 754–755. doi:10.1093/bioinformatics/17.8.754
Kerp H. 1984. Aspects of Permian palaeobotany and palynology. III. A new reconstruction of Lilpopia raciborskii (Lilpop) Conert et Schaarschmidt (Sphenopsida). Review of Palaeobotany and Palynology 40: 237–261. doi:10.1016/0034-6667(84)90011-3
Kerp H, Bomfleur B. 2011. Photography of plant fossils—New techniques, old tricks. Review of Palaeobotany and Palynology 166: 117–151. doi:10.1016/j.revpalbo.2011.05.001
King B. 2021. Bayesian tip-dated phylogenetics in paleontology: topological effects and stratigraphic fit. Systematic Biology 70: 283–294. doi:10.1093/sysbio/syaa057
Leclercq S. 1957. Etude d’une fructification de Sphenopsida à structure conservée du Devonian supérieur. Mémoires, l'Académie Royal de Belgique, Classe des Sciences, Collection 14: 1–39.
Leclercq S. 1969. Calamophyton primaevum: the complex morphology of its fertile appendage. American Journal of Botany 56: 773–781. doi:10.1002/j.1537-2197.1969.tb09725.x
Leclercq S, Banks HP. 1962. Pseudosporochnus nodosus sp. nov., a Middle Devonian plant with cladoxylalean affinities. Palaeontographica Abteilung B 110: 1–34.
Leisman GA, Graves C. 1964. The structure of the fossil sphenopsid cone, Peltastrobus reedae. The American Midland Naturalist 72: 426–437. doi:10.2307/2423515
Levittan ED, Barghoorn ES. 1948. Sphenostrobus thompsonii: a new genus of the Spenophyllales? American Journal of Botany 35: 350–358. doi:10.1002/j.1537-2197.1948.tb08091.x
Lewis PO. 2001. A likelihood approach to estimating phylogeny from discrete morphological character data. Systematic Biology 50: 913–925. doi:10.1080/106351501753462876
Li X, Cai C, Wang Y. 1995. Hamatophyton verticillatum (Gu and Zhi) emend. A primitive plant of sphenopsida from the upper Devonian- lower carboniferous in China. Palaeonto- Graphica Abteilung B: Palaeophytologie 235: 1–22.
Libertín M, Bek J, Drábková J. 2014. New sphenophyllaleans from the Pennsylvanian of the Czech Republic. Review of Palaeobotany and Palynology 200: 196–210. doi:10.1016/j.revpalbo.2013.09.008
Lilpop J. 1937. New plants from the Permo-Carboniferous rocks in Poland. International Bulletin of the Polish Academy of Sciences and Letters: Mathematical and Natural Sciences Class: Series B: Natural Sciences 1: 1–10.
Lipiarski I. 1971. La flore du Permien inférieur apparaissant dans le travertin de Karniowice aux environs de Cracovie. Prace—Panstwowego Instytutu Geologicznego 58: 5–112.
Lipiarski I. 1972. New data concerning the morphology of the fossil genus Lilpopia Conert et Schaarschmidt 1970 (= Tristachya Lilpop 1937). Acta Palaeobotanica 13: 101–109.
Liu L, Pšenička J, Bek J, Wan M, Pfefferkorn HW, Wang J. 2021. A whole calamitacean plant Palaeostachya guanglongii from the Asselian (Permian) Taiyuan Formation in the Wuda Coalfield, Inner Mongolia, China. Review of Palaeobotany and Palynology 294: 104245. doi:10.1016/j.revpalbo.2020.104245
Luo A, Duchêne DA, Zhang C, Zhu C, Ho SYW. 2020. A simulation-based evaluation of tip-dating under the fossilized birth–death process. Systematic Biology 69: 325–344. doi:10.1093/sysbio/syz038
Maddison WP, Maddison DR. 2011. Mesquite: a modular system for evolutionary analysis.
Mosbrugger V. 1990. The tree habit in land plants: a functional comparison of trunk constructions with a brief introduction into the biomechanics of trees. Journal of Evolutionary Biology 4: 516–517.
Nathorst AG. 1894. Zur paläozoischen Flora der arktischen Zone der Bäreninsel. Svenska Veten·skaps Akademiens Handlingar 26: 1–80.
Nathorst AG. 1902. Zur oberdevonischen Flora der Bäreninsel. Svenska Veten·skaps Akademiens Handlingar 36: 1–60.
Neregato R, Hilton J. 2019. Reinvestigation of the enigmatic carboniferous sphenophyte strobilus cheirostrobus scott and implications of in situ retusotriletes spores. International Journal of Plant Sciences 180: 811–833. doi:10.1086/704945
Neuberg MF. 1964. Permian flora of the Petchora Basin, part II. Sphenopsida [in Russian]. Trudy Geologicheskogo Instituta Akademii Nauk SSSR 30: 1–90.
Orlova OA, Jurina AL. 2014. A new articulate species, Pseudobornia schweitzeri Jurina et O. Orlova, sp. nov., from the Upper Devonian of Northern Timan, Russia. Paleontological Journal 48: 90–100. doi:10.1134/S0031030114010080
Prestianni C, Gess RW. 2019. Rinistachya hilleri gen. et sp. nov. (Sphenophyllales), from the upper Devonian of South Africa. Organisms Diversity & Evolution 19: 1–11. doi:10.1007/s13127-018-0385-3
R Core Team. 2022. R: a language and environment for statistical computing, Vol. 4.2.1. Vienna, Austria: R Foundation for Statistical Computing. https://www.R-project.org/.
Rothwell GW. 1999. Fossils and ferns in the resolution of land plant phylogeny. Botanical Review 65: 188–218. doi:10.1007/BF02857629
Rothwell GW, Taylor TN. 1971a. Studies of Paleozoic calamitean cones: Weissia kentuckiense gen. et sp. nov. Botanical Gazette 132: 215–224. doi:10.1086/336581
Rothwell GW, Taylor TN. 1971b. Weissistachys kentuckiensis: a new name for Weissia kentuckiense Rothwell and Taylor. Botanical Gazette 132: 371–372. doi:10.1086/336605
Schweitzer HJ. 1967. Die Oberdevon Flora der Bäreninsel: 1. Pseudobornia ursina Nathorst, Palaeontographica Abteilung B: Palaeophytologie 120: 116–137.
Schweitzer HJ. 1990. Pflanzen erobern das Land. Kleine Senckenberg-Reihe Frankfurt am Maine 18: 1–75.
Schweitzer HJ. 2003. Die Landnahme der Pflanzen. Decheniana (Bonn) 156: 177–215. doi:10.21248/decheniana.v156.4493
Schweitzer HJ. 2006. Die Oberdevon-Flora der Bäreninsel—5. Gesamtübersicht. Palaeon- Tographica Abteilung B: Palaeophytologie 274: 1–191. doi:10.1127/palb/274/2006/1
Skog J, Banks HP. 1973. Ibyka amphikoma, gen. et sp. nov., a new protoarticulate precursor from the late middle Devonian of New York state. American Journal of Botany 60: 366–380. doi:10.1002/j.1537-2197.1973.tb05937.x
Stein WE Jr, WightDC, Beck CB. 1984. Possible alternatives for the origin of Sphenopsida. Systematic Botany 9: 102–118. doi:10.2307/2418412
Stewart WN, Rothwell GW. 1993. Paleobotany and the evolution of plants. Cambridge, UK: Cambridge University Press.
Stur D. 1875. Die Culm-Flora des Mährisch-Schlesischen Dachschiefers. Abhandlungen der kaiserlich-königlichen geologischen Reichsanstalt 8: 1–106.
Stur D. 1877. Die Culm-Flora der Ostrauer und Waldenburger Schichten. Abhandlungen der kaiserlich-königlichen geologischen Reichsanstalt 8: 1–366.
Taylor TN, Taylor EL, Krings M. 2009. Paleobotany. The biology and evolution of fossil plants, 2nd ed. Amsterdam, Netherlands: Academic Press.
Tomescu AMF, Escapa IH, Rothwell GW, Elgorriaga A, Cúneo NR. 2017. Developmental programmes in the evolution of Equisetum reproductive morphology: a hierarchical modularity hypothesis. Annals of Botany 119: 489–505. doi:10.1093/aob/mcw273
Tomescu AMF, Whitewoods C. 2024. Development on the rocks: integrating molecular biology and the fossil record to reconstruct the evolution of leaf development. Perspectives in Plant Ecology, Evolution and Systematics 64: 125797. doi:10.1016/j.ppees.2024.125797
Wang Y. 1993. First discovery of Eviostachya hoegii Stockmans from Wutung Formation in China. Acta Palaeontologica Sinica 32: 430–441.
Wang DM. 2008. A new iridopteridalean plant from the middle Devonian of Northwest China. International Journal of Plant Sciences 169: 1100–1115. doi:10.1086/590445
Wang Z, Geng B. 1997. A new Middle Devonian plant: Metacladophyton tetraxylum gen. et sp. nov. Palaeontographica Abteilung B: Palaeophytologie 243: 85–102.
Wang D, Guo Y. 2009. Hamatophyton from the Late Devonian of Anhui Province, South China and evolution of Sphenophyllales. Acta Geologica Sinica 83: 492–503. doi:10.1111/j.1755-6724.2009.00070.x
Wang D, Hao S, Tian L, Xue J. 2006. Further study of the Late Devonian sphenopsid Hamatophyton verticillatum from China. International Journal of Plant Sciences 167: 885–896. doi:10.1086/503818
Worsley D, Agdestein T, Gjelberg JG, et al 2001. The geological evolution of Biørnøya, Arctic Norway: implications for the Barents Shelf. Norwegian Journal of Geology 81: 195–234.
Worsley D, Edwards MB. 1976. The upper Palaeozoic succession of Bjørnøya, Norsk Polarinst. Arbok 314: 163–176.
