Asteroxylon
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| Asteroxylon Fossil range: Early Devonian |
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Asteroxylon ("star-shaped xylem") is an extinct genus of plants of the Division Lycopodiophyta known from Early Devonian (~400 million year old) sediments in Britain, and is probably a stem group to the Drepanophycaceae.[citation needed]
[edit] Description
Asteroxylon is a terrestrial genus of vascular plant which flourished in the Early Devonian period. Dichotomously branching stems, which reached 12 mm in diameter and 40 cm in length, were erect, rising from a ground-running organ, from which also protruded underground "rhizoids" or "roots": these reached a depth of up to 20cm below the surface.[1] An actinostelic vascular bundle occupied the centre of the axes, with tracheids being of primitive annular or helical type (so-called G-type). "Leaves" - not true leaves, but protrusions - were of the form of unbranched strap-shaped enations up to 5 mm long; a single vascular trace branched from the main bundle in the centre of the stem to terminate at the base of each enation. Enations and axes bore stomata.
Asteroxylon differs from externally similar genera of the same period, Drepanophycus and Baragwanathia, as the vascular thread proceeding well into the leaf in these genera; see Drepanophycales for more details.
[edit] References
- ^ Smoot, E.L.; Jansen, R.K.; Taylor, T.N. (1981). "A Phylogenetic Analysis of the Land Plants: A Botanical Commentary". Taxon 30 (1): 65–67. doi:.
- Kidston R & Lang WH (1920) On Old Red Sandstone plants showing structure, from the Rhynie chert bed, Aberdeenshire. Part III. Asteroxylon mackiei, Kidston and Lang. Transactions of the Royal Society of Edinburgh 52, 643-680.
- The Rhynie Chert and Asteroxylon
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