Distichophytum is a genus of extinct vascular plants of the Late Silurian (Ludfordian) to Early Devonian (Emsian), around 426 to 393 million years ago. The genus has a tangled taxonomic history, also being known as Bucheria and Rebuchia (see below).
Stylized reconstruction of the habit of Distichophytum ovatum. Based on the information in Hueber 1972, but not the figure, which is more 'realistic'.
The genus was first discovered as fossils of Early Devonian age (Pragian or Siegenian to Emsian, 411 to 393 million years ago), consisting of isolated spikes of sporangia (spore-forming organs) found at Beartooth Butte, Wyoming, United States of America. Specimens of D. ovata with sporangia attached to stems were later found at the same location. The base of the plant remains unknown; the known part was about 8.5 cm high. The sporophyte consisted of narrow leafless stems (axes) 1.5 to 2.0 mm in diameter, which branched dichotomously. Stems which did not bear sporangia ended in blunt points; fertile branches bore compact one-sided spikes of up to 20 laterally attached sporangia, more-or-less opposite. The sporangia were kidney-shaped (reniform) and had short stalks around 1.5 mm long which curved so that all the sporangia were on one side of the stem. The sporangia split (dehisced) distally into two equal parts in order to release the unornamented spores.[2][4] Specimens from the Pragian flora of Bathurst Island, Nunavut, Canada, were later also assigned to this species, although their sporangia were smaller.[1]
A second possible species, D. mucronatum, has narrower, less branched stems and smaller, somewhat differently shaped sporangia than D. ovata. Hueber considered the differences in sporangial shape were caused by compression and that the other differences were too small to warrant a different species;[2] Schweitzer put the two in the same genus but as different species.[5] A third possible species was discovered in sediments from Bathurst Island, Nunavut, Canada, from the Late Silurian (Ludfordian, 426 to 423 million years ago); it was not assigned a species name as poor preservation obscured the sporangial shape.[1]
Taxonomyedit
The genus has a somewhat tangled taxonomic history which has been clarified by Kotyk et al.[1] The genus Bucheria Dorf was created in 1933 for what is now D. ovata.[6] Independently, Distichophytum Mägdefrau was created in 1938 for D. mucronatum.[3] Later, Bucheria Dorf was discovered to be homonym of Bucheria Heynhold of 1846, and the alternative Rebuchia (an anagram of Bucheria) was suggested provisionally by Høeg in 1967, but only as a form genus for poorly preserved spikes.[7]Rebuchia was formally established by Hueber in 1970 as a replacement for the invalid Bucheria Dorf.[2] However, Hueber regarded Bucheria ovata Dorf and Distichophytum mucronatum Mägdefrau as the same species; in which case the name Distichophytum had priority over his Rebuchia and should have been used as the genus name.[1]
Phylogenyedit
On the basis of the shape of the sporangia (reniform), their lateral position on the stem, borne on short stalks, and their mode of dehiscence, Hueber placed the genus in the Zosterophyllophytina. A cladogram published in 2004 by Crane et al. agrees in placing Distichophytum (as Rebuchia in the original) in a paraphyleticstem group of broadly defined "zosterophylls", basal to the lycopsids (living and extinct clubmosses and relatives).[8]
Hao and Xue in 2013 listed the genus as a zosterophyll.[9]
Referencesedit
^ abcdefKotyk, M.E.; Basinger, J.F.; Gensel, P.G. & de Freitas, T.A. (2002), "Morphologically complex plant macrofossils from the Late Silurian of Arctic Canada", Am. J. Bot., 89 (6): 1004–1013, doi:10.3732/ajb.89.6.1004, PMID 21665700
^ abcdHueber, F.M. (1972), "Rebuchia ovata, its vegetative morphology and classification with the Zosterophyllophytina", Review of Palaeobotany and Palynology, 14 (1–2): 113–127, doi:10.1016/0034-6667(72)90012-7
^ abcMägdefrau, K. (1938), "Eine Halophyten-Flora aus dem Unterdevon des Harzes", Beiheft zum Botanischen Centralblatt, 58b: 243–251 cited in Kotyk et al. 2002
^Taylor, T.N.; Taylor, E.L. & Krings, M. (2009), Paleobotany, The Biology and Evolution of Fossil Plants (2nd ed.), Amsterdam; Boston: Academic Press, ISBN978-0-12-373972-8, p. 258
^Schweitzer, H.-J. (1979), "Die Zosterophyllaceae des rheinischen Unterdevons", Bonner Paläobotanische Mitteilungen, 3: 1–32, cited in Kotyk et al. 2002
^Dorf, E. (1933), "A new occurrence of the oldest known terrestrial vegetation, from Beartooth Butte, Wyoming", Botanical Gazette, 95 (2): 240–257, doi:10.1086/334384, S2CID 83628574, cited in Hueber 1972
^Høeg, O.A. (1967), "Psilophyta", in Boureau, E. (ed.), Traité de Paléobotanique, vol. II, Paris: Masson et Compagnie, p. 191ff, cited in Hueber 1972
^Crane, P.R.; Herendeen, P. & Friis, E.M. (2004), "Fossils and plant phylogeny", American Journal of Botany, 91 (10): 1683–99, doi:10.3732/ajb.91.10.1683, PMID 21652317
^Hao, Shougang & Xue, Jinzhuang (2013), The early Devonian Posongchong flora of Yunnan: a contribution to an understanding of the evolution and early diversification of vascular plants, Beijing: Science Press, p. 329, ISBN978-7-03-036616-0, retrieved 2019-10-25
distichophytum, genus, extinct, vascular, plants, late, silurian, ludfordian, early, devonian, emsian, around, million, years, genus, tangled, taxonomic, history, also, being, known, bucheria, rebuchia, below, temporal, range, ludfordian, emsian, preꞒ, scienti. Distichophytum is a genus of extinct vascular plants of the Late Silurian Ludfordian to Early Devonian Emsian around 426 to 393 million years ago The genus has a tangled taxonomic history also being known as Bucheria and Rebuchia see below DistichophytumTemporal range Ludfordian Emsian 1 2 PreꞒ Ꞓ O S D C P T J K Pg N Scientific classification Kingdom Plantae Clade Tracheophytes Clade Lycophytes Plesion Zosterophylls Genus DistichophytumMagd 1938 3 Species D ovatum Dorf emend Hueber Schweitzer 1 D mucronatum Magd 3 For synonyms see the Taxonomy section of the article Contents 1 Description 2 Taxonomy 3 Phylogeny 4 References 5 External linksDescription edit nbsp Stylized reconstruction of the habit of Distichophytum ovatum Based on the information in Hueber 1972 but not the figure which is more realistic The genus was first discovered as fossils of Early Devonian age Pragian or Siegenian to Emsian 411 to 393 million years ago consisting of isolated spikes of sporangia spore forming organs found at Beartooth Butte Wyoming United States of America Specimens of D ovata with sporangia attached to stems were later found at the same location The base of the plant remains unknown the known part was about 8 5 cm high The sporophyte consisted of narrow leafless stems axes 1 5 to 2 0 mm in diameter which branched dichotomously Stems which did not bear sporangia ended in blunt points fertile branches bore compact one sided spikes of up to 20 laterally attached sporangia more or less opposite The sporangia were kidney shaped reniform and had short stalks around 1 5 mm long which curved so that all the sporangia were on one side of the stem The sporangia split dehisced distally into two equal parts in order to release the unornamented spores 2 4 Specimens from the Pragian flora of Bathurst Island Nunavut Canada were later also assigned to this species although their sporangia were smaller 1 A second possible species D mucronatum has narrower less branched stems and smaller somewhat differently shaped sporangia than D ovata Hueber considered the differences in sporangial shape were caused by compression and that the other differences were too small to warrant a different species 2 Schweitzer put the two in the same genus but as different species 5 A third possible species was discovered in sediments from Bathurst Island Nunavut Canada from the Late Silurian Ludfordian 426 to 423 million years ago it was not assigned a species name as poor preservation obscured the sporangial shape 1 Taxonomy editThe genus has a somewhat tangled taxonomic history which has been clarified by Kotyk et al 1 The genus Bucheria Dorf was created in 1933 for what is now D ovata 6 Independently Distichophytum Magdefrau was created in 1938 for D mucronatum 3 Later Bucheria Dorf was discovered to be homonym of Bucheria Heynhold of 1846 and the alternative Rebuchia an anagram of Bucheria was suggested provisionally by Hoeg in 1967 but only as a form genus for poorly preserved spikes 7 Rebuchia was formally established by Hueber in 1970 as a replacement for the invalid Bucheria Dorf 2 However Hueber regarded Bucheria ovata Dorf and Distichophytum mucronatum Magdefrau as the same species in which case the name Distichophytum had priority over his Rebuchia and should have been used as the genus name 1 Phylogeny editOn the basis of the shape of the sporangia reniform their lateral position on the stem borne on short stalks and their mode of dehiscence Hueber placed the genus in the Zosterophyllophytina A cladogram published in 2004 by Crane et al agrees in placing Distichophytum as Rebuchia in the original in a paraphyletic stem group of broadly defined zosterophylls basal to the lycopsids living and extinct clubmosses and relatives 8 lycophytes Hicklingia basal groups Adoketophyton Discalis Distichophytum Rebuchia Gumuia Huia Zosterophyllum myretonianum Z llanoveranum Z fertile core zosterophylls Zosterophyllum divaricatum Tarella Oricilla Gosslingia Hsua Thrinkophyton Protobarinophyton Barinophyton obscurum B citrulliforme Sawdonia Deheubarthia Konioria Anisophyton Serrulacaulis Crenaticaulis basal groups Nothia Zosterophyllum deciduum lycopsids extant and extinct members Hao and Xue in 2013 listed the genus as a zosterophyll 9 References edit a b c d e f Kotyk M E Basinger J F Gensel P G amp de Freitas T A 2002 Morphologically complex plant macrofossils from the Late Silurian of Arctic Canada Am J Bot 89 6 1004 1013 doi 10 3732 ajb 89 6 1004 PMID 21665700 a b c d Hueber F M 1972 Rebuchia ovata its vegetative morphology and classification with the Zosterophyllophytina Review of Palaeobotany and Palynology 14 1 2 113 127 doi 10 1016 0034 6667 72 90012 7 a b c Magdefrau K 1938 Eine Halophyten Flora aus dem Unterdevon des Harzes Beiheft zum Botanischen Centralblatt 58b 243 251 cited in Kotyk et al 2002 Taylor T N Taylor E L amp Krings M 2009 Paleobotany The Biology and Evolution of Fossil Plants 2nd ed Amsterdam Boston Academic Press ISBN 978 0 12 373972 8 p 258 Schweitzer H J 1979 Die Zosterophyllaceae des rheinischen Unterdevons Bonner Palaobotanische Mitteilungen 3 1 32 cited in Kotyk et al 2002 Dorf E 1933 A new occurrence of the oldest known terrestrial vegetation from Beartooth Butte Wyoming Botanical Gazette 95 2 240 257 doi 10 1086 334384 S2CID 83628574 cited in Hueber 1972 Hoeg O A 1967 Psilophyta in Boureau E ed Traite de Paleobotanique vol II Paris Masson et Compagnie p 191ff cited in Hueber 1972 Crane P R Herendeen P amp Friis E M 2004 Fossils and plant phylogeny American Journal of Botany 91 10 1683 99 doi 10 3732 ajb 91 10 1683 PMID 21652317 Hao Shougang amp Xue Jinzhuang 2013 The early Devonian Posongchong flora of Yunnan a contribution to an understanding of the evolution and early diversification of vascular plants Beijing Science Press p 329 ISBN 978 7 03 036616 0 retrieved 2019 10 25External links editCladogram from Crane Herendeen amp Friis 2004 Retrieved from https en wikipedia org w index php title Distichophytum amp oldid 1193404515, wikipedia, wiki, book, books, library,
