Scheckler, Stephen E. , Skog, Judith E. .
Langoxylon asterochlaenoideum (Stockmans1968): a fern-like plant from the Middle Devonian of Belgium.
Restudy of Middle Devonian Langoxylon anatomy helps to clarify its relationships. Main axes have a large multi-ribbed actinostele from which helical traces depart to laterals. Most are branches supplied by terete traces that expand distally, become bilaterally ridged, and then radially fluted just before branch separation. Other leaf-like appendages are supplied by smaller terete traces that fork and contract distally. Cortex has inner parenchymatous and outer fibrous zones. Inner metaxylem of main axis and branches consists mostly of parenchyma. Mesarch protoxylem strands are of two types. Main axis protoxylem consists of tracheids. Lateral appendage protoxylem has a core of parenchyma cells surrounded by tracheids with minimal cell elongation. This differs from protoxylem lacunae of similar taxa where parenchyma is absent and stretching and destruction of central tracheids produce a vertical cavity. Protoxylem architecture thus appears useful for systematics of early fern-like plants. Langoxylon only superficially resembles Asteropteris and Asterochlaena, to which Stockmans compared his genus, and seems to be unrelated to them or to iridopterids (e.g., Ibyka, Arachnoxylon, Iridopteris, Compsocradus) or the possible lignophyte Stenokoleos. Langoxylon compares best with Actinopodium and Actinoxylon, Middle Devonian archaeopterid progymnosperms. We believe, however, that Langoxylon is a fern-like Middle Devonian euphyllophyte of uncertain affinities.
1 - Virginia Polytechnic Institute and State University (Virginia Tech), Departments of Biology and Geological Sciences, Blacksburg, Virginia, 24061-0406, USA
2 - George Mason University, Department of Environmental Science and Policy 5F2, Fairfax, Virginia, 22030-4444, USA
Presentation Type: Paper
Location: Maybird (Cliff Lodge)
Date: Monday, August 2nd, 2004
Time: 9:00 AM