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FOLIAR MORPHOLOGY AND ANATOMY OF THE GIGANTOPTERID PLANT DELNORTEA ABBOTTIAE, FROM THE LOWER PERMIAN OF WEST TEXAS
Author(s) -
Mamay Sergius H.,
Miller John M.,
Rohr David M.,
Stein William E.
Publication year - 1988
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1988.tb14202.x
Subject(s) - biology , petiole (insect anatomy) , xylem , genus , permian , tracheid , botany , taxon , paleontology , incertae sedis , morphology (biology) , structural basin
Delnortea is a monotypic genus (type‐species: D. abbottiae) of Lower Permian gymnosperms based on leaves from uppermost Leonardian deltaic sediments exposed in the Del Norte Mountains, West Texas. The leaves are simple, symmetrical, mostly oblong or elliptical, and vary in length from 1.2 to about 35 cm. The petioles are short and stout, with a basally enlarged abscission zone. The margins are crenate, with a narrow, indurated border. Venation is in 4 orders: the secondaries and tertiaries are robust, unbranched, and pinnately arranged in a precise “herringbone” pattern, with the secondaries ending in the marginal sinuses; the quaternaries divide sparingly and fuse with others to form a dense reticulum of small meshes. Permineralized petiole and midrib material reflects a bifacial cambium, shown by a semicircular vascular arc, irregularly divided into several collateral bundles with secondary xylem and phloem. Delnortea is referable to the Gigantopteridaceae, a probably artificial family of gymnosperms incertae sedis with important venation features in common, but without known diagnostic reproductive organs. With Delnortea , the North American gigantopterids now include 5 genera, but Gigantopteris itself is lacking. Delnortea holds a relatively advanced evolutionary position among the American gigantopterids; its leaf morphology and gymnospermous anatomy entail intriguing points of comparison with Gnetum. The limited geographic and stratigraphic ranges and morphological distinctiveness of the American gigantopterids and associated taxa attest to rapid evolution and dispersal from a small area of origin in the southwestern United States during Leonardian time.