Isoetales

Isoetales, sometimes also written Isoëtales, is an order of plants in the class Lycopodiopsida.

Isoetales
Isoetes
Pleuromeia
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Lycophytes
Class: Lycopodiopsida
Order: Isoetales
Prantl
Families

Chaloneriaceae†
Isoetaceae
Pleuromeiaceae†
Nathorstianaceae†

There are about 140-150 living species, all of which are classified in the genus Isoetes (quillworts), with a cosmopolitan distribution, but often scarce to rare. Living species are mostly aquatic or semi-aquatic, and are found in clear ponds and slowly moving streams. Each leaf is slender and broadens downward to a swollen base up to 5 mm wide where the leaves attach in clusters to a bulb-like, underground corm characteristic of most quillworts. This swollen base also contains male and female sporangia, protected by a thin, transparent covering (velum), which is used diagnostically to help identify quillwort species. Quillwort species are very difficult to distinguish by general appearance. The best way to identify them is by examining the megaspores under a microscope.

Isoetes are the only living pteridophytes capable of secondary growth.[1]

Fossils

Some authors include the tree-like "aboresecent lycophytes", which formed forests during the Carboniferous period, and often assigned to their own order, Lepidodendrales, within Isoetales.[2]

Fossilised specimens of Isoetes beestonii have been found in rocks dating to the latest Permian-earliest Triassic.[3][4] During the Early Triassic, Isoetales, such as the long-stemmed Pleuromeia were dominant over large areas of the globe.[5] The oldest fossil closely resembling modern quillworts is Isoetites rolandii from the Late Jurassic of North America.[6]

References
  1. Karrfalt, Eric E. (1982-12-01). "Secondary Development in the Cortex of Isoetes". Botanical Gazette. 143 (4): 439–445. doi:10.1086/337319. ISSN 0006-8071. S2CID 84969975.
  2. Bateman, Richard M.; DiMichele, William A. (October 2021). "Escaping the voluntary constraints of "tyre‐track" taxonomy". Taxon. 70 (5): 1062–1077. doi:10.1002/tax.12540. ISSN 0040-0262. S2CID 238818487.
  3. Retallack, Gregory J. (1997). "Earliest Triassic origin of Isoetes and quillwort evolutionary radiation". Journal of Paleontology. 7 (3): 500–521. doi:10.1017/S0022336000039524. S2CID 140566050.
  4. Retallack, Gregory J. (2013). "Permian and Triassic greenhouse crises". Gondwana Research. 24 (1): 90–103. Bibcode:2013GondR..24...90R. doi:10.1016/j.gr.2012.03.003.
  5. Looy, Cindy V.; van Konijnenburg-van Cittert, Johanna H. A.; Duijnstee, Ivo A. P. (2021). "Proliferation of Isoëtalean Lycophytes During the Permo-Triassic Biotic Crises: A Proxy for the State of the Terrestrial Biosphere". Frontiers in Earth Science. 9: 55. Bibcode:2021FrEaS...9...55L. doi:10.3389/feart.2021.615370. ISSN 2296-6463.
  6. Wood, Daniel; Besnard, Guillaume; Beerling, David J.; Osborne, Colin P.; Christin, Pascal-Antoine (2020-06-18). Wong, William Oki (ed.). "Phylogenomics indicates the "living fossil" Isoetes diversified in the Cenozoic". PLOS ONE. 15 (6): e0227525. Bibcode:2020PLoSO..1527525W. doi:10.1371/journal.pone.0227525. ISSN 1932-6203. PMC 7302493. PMID 32555586.
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