Figure 1. Artistic representation of a Carboniferous forest
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The quillworts (Order Isoetales, Subphylum Lycopodiophytina) are the extant remnant of an order that included the great trees of the Carboniferous coal swamps (illustrated in Figure 1 on the left). These trees could reach heights of almost 50 meters with trunk diameters of up to 2 meters (Boyce and DiMichele, 2018). Budke et al (2005) provide a helpful description of the anatomy of the extant isoetales.
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Few phylogenetic trees of the stem-Isoteales have been published. The time tree below represents a combination of two fairly recent ones (although the part pertaining to the Lepidodendrales, which are in a sister relationship to the crown-Isoetales, is essentially based on work by Bateman et al, 1992):
Figure 2. Time tree of the stem-Isoetales
The oldest known member of the stem-Isoetales is Yuguangia ordinata, found in the upper part of the Haikou Formation of the Middle Devonian (late Givetian) at Yuguang village, Zhanyi District of Yunnan Province, southwestern China (Hao et al, 2007; Gerrienne et al, 2018). No image of this fossil is available in the public domain, but other members of the stem group are shown below (click on image for a larger view):
Figure 3. Images of stem-Isoetales
All the above images, except for Lilingostrobus chaloneri, belong to the Lepidendrolales, or arborescent lycophytes, which formed extensive forests in the equatorial coal swamps of the Late Carboniferous (Thomas and Cleal, 2018). No trends can be discerned in the above set of images.
There is uncertainty concerning the oldest known member of the isoetalean crown group. As stated by Wikström et al (2023), “Isoetes‐like fossil plants described from the Mesozoic and the Cenozoic cannot be unequivocally placed within the crown group of extant species”. Furthermore, there is some contradiction in the literature: Retallack (1997) presents the Early Triassic fossil Isoetes beestonii as the most ancient known species of the living genus Isoetes, while Pereira et al (2017) state that Isoetites rolandii, of Late Jurassic age, is the earliest fossil known that is assigned to the family Isoetaceae. We will take the conservative view that Isoetites rolandii is more likely to represent the oldest known member of the crown-Isoetales. The fossil was found in the Late Jurassic Coon Hollow Formation at Hells Canyon in the Pittsburg Landing area, Oregon and Idaho, USA (Ash and Pigg, 1991; Pereira et al, 2017). Unfortunately, no image of this fossil is available in the public domain.
The available fossil data indicate that the Isoetales stem group developed from Middle Devonian to Late Jurassic time, representing a long stem-to-crown transition of between 219 and 240 million years (see Figure 1). However, assuming that the oldest member of the crown group is the Early Triassic Isoetes beestonii would imply a stem-to-crown transition of between 131 and 138 million years.
There is uncertainty concerning the oldest known member of the isoetalean crown group. As stated by Wikström et al (2023), “Isoetes‐like fossil plants described from the Mesozoic and the Cenozoic cannot be unequivocally placed within the crown group of extant species”. Furthermore, there is some contradiction in the literature: Retallack (1997) presents the Early Triassic fossil Isoetes beestonii as the most ancient known species of the living genus Isoetes, while Pereira et al (2017) state that Isoetites rolandii, of Late Jurassic age, is the earliest fossil known that is assigned to the family Isoetaceae. We will take the conservative view that Isoetites rolandii is more likely to represent the oldest known member of the crown-Isoetales. The fossil was found in the Late Jurassic Coon Hollow Formation at Hells Canyon in the Pittsburg Landing area, Oregon and Idaho, USA (Ash and Pigg, 1991; Pereira et al, 2017). Unfortunately, no image of this fossil is available in the public domain.
The available fossil data indicate that the Isoetales stem group developed from Middle Devonian to Late Jurassic time, representing a long stem-to-crown transition of between 219 and 240 million years (see Figure 1). However, assuming that the oldest member of the crown group is the Early Triassic Isoetes beestonii would imply a stem-to-crown transition of between 131 and 138 million years.
References
Ash, S. R., & Pigg, K. B. (1991). A new Jurassic Isoetites (Isoetales) from the Wallowa Terrane in Hells Canyon, Oregon and Idaho. American Journal of Botany, 78(12), 1636-1642.
Bateman, R. M., DiMichele, W. A., & Willard, D. A. (1992). Experimental cladistic analysis of anatomically preserved arborescent lycopsids from the Carboniferous of Euramerica: an essay on paleobotanical phylogenetics. Annals of the Missouri Botanical Garden, 500-559.
Boyce, C. K., & DiMichele, W. A. (2018). Fast or slow for the arborescent lycopsids?. New Phytologist, 218(3), 891-893.
Budke, J. M., Hickey, R. J., & Heafner, K. D. (2005). Analysis of morphological and anatomical characteristics of Isoetes using Isoetes tennesseensis. Brittonia, 57(2), 167-182.
Gerrienne, P., Cascales-Minana, B., Prestianni, C., Steemans, P., & Cheng-Sen, L. (2018). Lilingostrobus chaloneri gen. et sp. nov., a Late Devonian woody lycopsid from Hunan, China. Plos one, 13(7), e0198287.
Hao, S., Xue, J., Wang, Q., & Liu, Z. (2007). Yuguangia ordinata gen. et sp. nov., a new lycopsid from the Middle Devonian (late Givetian) of Yunnan, China, and its phylogenetic implications. International journal of plant sciences, 168(8), 1161-1175.
Hickey, R. J. (1986). The early evolutionary and morphological diversity of Isoetes, with descriptions of two new Neotropical species. Systematic Botany, 309-321.
Pereira, J. B., Labiak, P. H., Stützel, T., & Schulz, C. (2017). Origin and biogeography of the ancient genus Isoëtes with focus on the Neotropics. Botanical Journal of the Linnean Society, 185(2), 253-271.
Retallack, G. J. (1997). Earliest Triassic origin of Isoetes and quillwort evolutionary radiation. Journal of Paleontology, 71(3), 500-521.
Sand-Jensen, K., Prahl, C., & Stokholm, H. (1982). Oxygen release from roots of submerged aquatic macrophytes. Oikos, 349-354.
Strullu-Derrien, C., Servais, T., & Kenrick, P. (2023). Insights into palaeobotany. Botany Letters, 170(2), 157-164.
Taylor, W. C., & Hickey, R. J. (1992). Habitat, evolution, and speciation in Isoetes. Annals of the Missouri Botanical Garden, 613-622.
Thomas, B. A., & Cleal, C. J. (2018). Arborescent lycophyte growth in the late Carboniferous coal swamps. New Phytologist, 218(3), 885-890.
Wikström, N., Larsén, E., Khodabandeh, A., & Rydin, C. (2023). No phylogenomic support for a Cenozoic origin of the “living fossil” Isoetes. American Journal of Botany, 110(1), e16108.
Bateman, R. M., DiMichele, W. A., & Willard, D. A. (1992). Experimental cladistic analysis of anatomically preserved arborescent lycopsids from the Carboniferous of Euramerica: an essay on paleobotanical phylogenetics. Annals of the Missouri Botanical Garden, 500-559.
Boyce, C. K., & DiMichele, W. A. (2018). Fast or slow for the arborescent lycopsids?. New Phytologist, 218(3), 891-893.
Budke, J. M., Hickey, R. J., & Heafner, K. D. (2005). Analysis of morphological and anatomical characteristics of Isoetes using Isoetes tennesseensis. Brittonia, 57(2), 167-182.
Gerrienne, P., Cascales-Minana, B., Prestianni, C., Steemans, P., & Cheng-Sen, L. (2018). Lilingostrobus chaloneri gen. et sp. nov., a Late Devonian woody lycopsid from Hunan, China. Plos one, 13(7), e0198287.
Hao, S., Xue, J., Wang, Q., & Liu, Z. (2007). Yuguangia ordinata gen. et sp. nov., a new lycopsid from the Middle Devonian (late Givetian) of Yunnan, China, and its phylogenetic implications. International journal of plant sciences, 168(8), 1161-1175.
Hickey, R. J. (1986). The early evolutionary and morphological diversity of Isoetes, with descriptions of two new Neotropical species. Systematic Botany, 309-321.
Pereira, J. B., Labiak, P. H., Stützel, T., & Schulz, C. (2017). Origin and biogeography of the ancient genus Isoëtes with focus on the Neotropics. Botanical Journal of the Linnean Society, 185(2), 253-271.
Retallack, G. J. (1997). Earliest Triassic origin of Isoetes and quillwort evolutionary radiation. Journal of Paleontology, 71(3), 500-521.
Sand-Jensen, K., Prahl, C., & Stokholm, H. (1982). Oxygen release from roots of submerged aquatic macrophytes. Oikos, 349-354.
Strullu-Derrien, C., Servais, T., & Kenrick, P. (2023). Insights into palaeobotany. Botany Letters, 170(2), 157-164.
Taylor, W. C., & Hickey, R. J. (1992). Habitat, evolution, and speciation in Isoetes. Annals of the Missouri Botanical Garden, 613-622.
Thomas, B. A., & Cleal, C. J. (2018). Arborescent lycophyte growth in the late Carboniferous coal swamps. New Phytologist, 218(3), 885-890.
Wikström, N., Larsén, E., Khodabandeh, A., & Rydin, C. (2023). No phylogenomic support for a Cenozoic origin of the “living fossil” Isoetes. American Journal of Botany, 110(1), e16108.
Image credits – Stem-Isoetales
- Header (Spiny-spored quillwort, Isoetes echinospora): Valerii Glazunov, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
- Figure 1: ABelov2014, under Attribution 3.0 Unported (CC BY 3.0) license
- Figure 3 (Lilingostrobus chaloneri): Open Access article Gerrienne, P., Cascales-Minana, B., Prestianni, C., Steemans, P., & Cheng-Sen, L. (2018). Lilingostrobus chaloneri gen. et sp. nov., a Late Devonian woody lycopsid from Hunan, China. Plos one, 13(7), e0198287.
- Figure 3 (Paralycopodites sp.): Open Access article Bateman, R. M., & DiMichele, W. A. (2021). Escaping the voluntary constraints of “tyre‐track” taxonomy. Taxon, 70(5), 1062-1077.
- Figure 3 (Sigillaria sp., fossil): Ashley Dace / Stanhope Tree, licensed for reuse under the Creative Commons Attribution-ShareAlike 2.0 license.
- Figure 3 (Sigillaria sp., life restoration): Falconaumanni, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
- Figure 3 (Synchysidendron sp., fossil): Open Access article Bateman, R. M., & DiMichele, W. A. (2021). Escaping the voluntary constraints of “tyre‐track” taxonomy. Taxon, 70(5), 1062-1077.
- Figure 3 (Synchysidendron sp., life restoration): Falconaumanni, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
- Figure 3 (Diaphorodendron sp.): Open Access article Bateman, R. M., & DiMichele, W. A. (2021). Escaping the voluntary constraints of “tyre‐track” taxonomy. Taxon, 70(5), 1062-1077.
- Figure 3 (Lepidodendron sp., fossil): Photographed by Bob James (owner of website) at National Museum of Nature and Science, Tokyo, Japan, April 2023.
- Figure 3 (Lepidodendron sp., life restoration): Open Access article Wang, Q., Xu, H., & Shen, S. (2013). Notes on the Key Taxonomic Characters of Arborescent Lycopsid Stem Adpressions.
- Figure 3 (Lepidophloios sp., fossil): Verisimilus, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons
- Figure 3 (Lepidophloios sp., life restoration): Falconaumanni, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons