Cladus: Eukaryota Asteroxylon ("star-shaped xylem") is an extinct genus of plants of the Division Lycopodiophyta known from anatomically preserved specimens in an Early Devonian deposit of chert at Rhynie, Aberdeenshire in North-East Scotland[1] that has been dated at 396 ± 8 million years ago.[2] Asteroxylon is probably a stem group to the Drepanophycaceae. 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 20 cm below the surface.[3] 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.
References 1. ^ Kidston R & Lang WH (1920) On Old red sandstone plants showing structure from the Rhynie chert bed, Aberdeenshire. Part III. Asteroxylon mackiei, Kidston & Lang. Transactions of the Royal Society of Edinburgh 52, 643-680 * The Rhynie Chert and Asteroxylon Source: Wikipedia, Wikispecies: All text is available under the terms of the GNU Free Documentation License |
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