Hicklingia is a genus of extinct plants of the Middle Devonian (around 393 to 383 million years ago). Compressed specimens were first described in 1923 from the Old Red Sandstone of Scotland.[1] Initially the genus was placed in the "rhyniophytes", but this group is defined as having terminal sporangia (spore-forming organs), and later work showed that the sporangia of Hicklingia were lateral rather than strictly terminal, so that it is now regarded as having affinities with the zosterophylls.[2]
The sporophyte had a tufted growth habit, with narrow leafless stems (axes) up to 17 cm high which branched dichotomously. Sporangia were borne on short stalks (up to 3 mm), on all sides of the stem and also terminally. There are oval scars on specimens where the stalks are presumed to have broken off. The lateral sporangia were closely adpressed to the stem. The effect is of a 'spike' of sporangia which terminates some stems. The sporangia opened via slits, but these did not have the thickened borders which are a feature of some Zosterophyllum species. The vascular system of the stem was not observed.[2]Spores are up to 50 µm in diameter and trilete.[3] The gametophyte is not known.
Phylogenyedit
The affinity with zosterophylls is recognized in the cladogram published in 2004 by Crane et al. in which Hicklingia is placed as a sister to all the other lycophytes (living and extinct clubmosses and relatives).[4]
Hao and Xue in 2013 listed the genus as a zosterophyll.[5]
Referencesedit
^ abKidston, R. & Lang, W.H. (1923), "Notes on fossil plants from the Old Red Sandstone of Scotland, I. Hicklingia edwardii, K. and L.", Transactions of the Royal Society of Edinburgh, 53: 405–7, doi:10.1017/s0080456800004087, cited in Edwards 1976
^ abEdwards, D. (1976), "The systematic position of Hicklingia edwardii Kidston and Lang", New Phytol., 76: 173–181, doi:10.1111/j.1469-8137.1976.tb01449.x
^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. 254
^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
hicklingia, genus, extinct, plants, middle, devonian, around, million, years, compressed, specimens, were, first, described, 1923, from, sandstone, scotland, initially, genus, placed, rhyniophytes, this, group, defined, having, terminal, sporangia, spore, form. Hicklingia is a genus of extinct plants of the Middle Devonian around 393 to 383 million years ago Compressed specimens were first described in 1923 from the Old Red Sandstone of Scotland 1 Initially the genus was placed in the rhyniophytes but this group is defined as having terminal sporangia spore forming organs and later work showed that the sporangia of Hicklingia were lateral rather than strictly terminal so that it is now regarded as having affinities with the zosterophylls 2 HicklingiaTemporal range Middle Devonian PreꞒ Ꞓ O S D C P T J K Pg NScientific classificationKingdom PlantaeClade StreptophytaClade EmbryophytesClade PolysporangiophytesClade TracheophytesClade LycophytesPlesion Zosterophylls Genus HicklingiaKidst amp W H Lang 1923 1 Type speciesHicklingia edwardiiKidst amp W H Lang 1923 Species H edwardii Kidst amp W H Lang 1923 H erecta Krausel amp Weyland 1929 Contents 1 Description 2 Phylogeny 3 References 4 External linksDescription editThe sporophyte had a tufted growth habit with narrow leafless stems axes up to 17 cm high which branched dichotomously Sporangia were borne on short stalks up to 3 mm on all sides of the stem and also terminally There are oval scars on specimens where the stalks are presumed to have broken off The lateral sporangia were closely adpressed to the stem The effect is of a spike of sporangia which terminates some stems The sporangia opened via slits but these did not have the thickened borders which are a feature of some Zosterophyllum species The vascular system of the stem was not observed 2 Spores are up to 50 µm in diameter and trilete 3 The gametophyte is not known Phylogeny editThe affinity with zosterophylls is recognized in the cladogram published in 2004 by Crane et al in which Hicklingia is placed as a sister to all the other lycophytes living and extinct clubmosses and relatives 4 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 5 References edit a b Kidston R amp Lang W H 1923 Notes on fossil plants from the Old Red Sandstone of Scotland I Hicklingia edwardii K and L Transactions of the Royal Society of Edinburgh 53 405 7 doi 10 1017 s0080456800004087 cited in Edwards 1976 a b Edwards D 1976 The systematic position of Hicklingia edwardii Kidston and Lang New Phytol 76 173 181 doi 10 1111 j 1469 8137 1976 tb01449 x 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 254 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 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 Hicklingia amp oldid 1193404621, wikipedia, wiki, book, books, library,
