Horneophyton

taxobox
fossil_range=Silurian-DevonianVerify source|date=January 2008
regnum = Plantae
divisio = unassigned
classis = Horneophytopsida
genus= "Horneophyton"
genus_authority = Kidston & Lang 1920 "emend." Barghoorn & Darrah 1938
species = "H. lignieri"
binomial = "Horneophyton lignieri"
synonyms ="Hornea"

"Horneophyton" was an early plant which may form a "missing link" between the "rhyniophytes" and hornworts. It is among the most abundant organisms found in the Rhynie chert.

History

Its original generic name "Hornea" [Kidston, R. & Lang, W. H. 1920 On Old Red Sandstone plants showing structure, from the Rhynie chert bed, Aberdeenshire. Part II. Additional notes on Rhynia gwynne-vaughani Kidston and Lang; with descriptions of Rhynia major, n.sp., and Hornia lignieri, n.g., n.sp. Transactions of the Royal Society of Edinburgh, 52(24): 603-627.] transpired to be a synonym, leading to the plant's renaming. [Barghoorn, E. S. & Darrah, W. C. 1938. Horneophyton a necessary change of name for Hornea. Harvard University Botanical Museum Leaflets, 6: 142-144.]

Morphology

The female gametophyte of the plant has been recognised and described as the form taxon "Langiophyton mackiei".cite journal
author = Remy, W.
coauthors = Hass, H.
year = 1991
title = "Langiophyton mackiei" nov. gen., nov. spec., ein Gametophyt mit Archegoniophoren aus dem Chert von Rhynie (Unterdevon Schottland)
journal = Argumenta Palaeobotanica
volume = 8
language= German
pages = 69–117] It grew to a height of around 6 cm, and was free living.

Early stages of development of the sporophytes of "Horneophyton" (as of hornworts) may have been dependent on their parent gametophytes for nutrition, but mature specimens have expanded, corm-like bases to their stems that bore rhizoids and appear to be anchored in soil, suggesting a capacity for independent existence after the gametophyte had degenerated. The sporophyte had unornamented axes about 2 mm in diameter with an undivided cortex, and stomata were rare. There was a thin central strand of vascular tissue, reinforced with spiral and reticulate thickeningsFact|date=February 2008. They bore terminal sporangia, occasionally branched, which contained a central collumella, analogous to the sporangia of hornworts; however, hornworts' sporangia do not dichotomise.

Habitat

"Horneophyton" grew on sandy, organic-rich soil in damp to wet locations. They usually grew as isolated individuals. [Paul Selden, John Nudds: "Fenster zur Evolution. Berühmte Fossilfundstellen der Welt". Elsevier Spektrum Akademischer Verlag, München 2007, S. 53. ISBN 978-3-8274-1771-8]

Phylogeny

clade/sandbox|title=TITLE|caption=A possible phylogeny of Horneophyton|boxed=1|1= Liverworts|2= clade|1= Mosses|2= clade|1= Hornworts|label2= Polysporangiophytes|2= clade|1= "Horneophyton"|2= Tracheophytes (vascular plants) With vascular tissue but "bryophyte"-like alternation of phases and sporangia, the organism has been considered a missing link between the hornworts and tracheophytes (which molecular data suggest are sister groups).cite journal
author = Qiu, Y.L.
coauthors = Li, L.; Wang, B.; Chen, Z.; Knoop, V.; Groth-malonek, M.; Dombrovska, O.; Lee, J.; Kent, L.; Rest, J.; Others,
year = 2006
title = The deepest divergences in land plants inferred from phylogenomic evidence
journal = Proceedings of the National Academy of Sciences
volume = 103
issue = 42
pages = 15511
doi = 10.1073/pnas.0603335103]

Features suggesting a close relationship with the hornworts include the form of its sporangia; its corm also resembles the foot of some hornworts. The free living nature of sporophytes, and the fact that they display branching, are marked differences which force it into the stem group.

External links

* [http://www.abdn.ac.uk/rhynie/horneo.htm Horneophyton] at the University of Aberdeen. Includes images.

References