Mamay, Sergius H. U.S. Geological Survey, National Museum, Washington, DC.
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An extinct order of articulate land plants, common during Late Pennsylvanian and Early Permian times. They are typified by Sphenophyllum (see illustration), a small, branching plant, probably of trailing habit. The long, jointed stems rarely exceeded 0.4 in. (1 cm) in diameter and had superposed, longitudinal, surficial ribs between nodes. The vascular system contained a solid xylem core with triangular primary wood. The leaves were wedge-shaped, usually shorter than 0.8 in. (2 cm), and had toothed, notched, or rounded distal margins. They were attached at the nodes by their narrow ends, in whorls of usually 6 or 9 leaves each, rarely 18. Long, terminal cones, usually called Bowmanites when found detached, contained sporangia and spores. The sporangia terminated slender stalks, forming concentric whorls that alternated with whorls of sterile bracts. Most species were homosporous (producing spores of a single type). See also: Paleobotany; Plant kingdom; Sphenophyta
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