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Studies of Paleozoic Seed Ferns: Anatomy and Morphology of Morphology of Microspermopteris aphyllum

Thomas N. Taylor and Ruth A. Stockey
American Journal of Botany
Vol. 63, No. 10 (Nov. - Dec., 1976), pp. 1302-1310
Stable URL: http://www.jstor.org/stable/2441838
Page Count: 9
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Studies of Paleozoic Seed Ferns: Anatomy and Morphology of Morphology of Microspermopteris aphyllum
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Abstract

The discovery of numerous specimens of the monostelic pteridosperm genus Microspermopteris in Pennsylvanian coal ball petrifactions from the Lewis Creek and What Cheer localities provides additional information about the anatomical and morphological variability within the genus. Specimens are now known up to 1.1 cm in diam that bear epidermal appendages in the form of variously-shaped trichomes. The external surface of the stem is further ornamented by longitudinal flaps of cortical tissue. Petioles exhibiting a single C-shaped vascular strand with abaxial protoxylem are produced in a 2/5 phyllotaxy. Large petiole bases that clasp the stem produce primary pinnae alternately. The presence of axillary branching appears similar to that reported in Callistophyton and Lyginopteris. Triarch to polyarch adventitious roots, some with secondary tissues, are produced at both nodal and internodal regions. Of the currently recognized monostelic seed fern genera, Microspermopteris is most similar to Heterangium. Information is presented that supports current ideas regarding the evolution of the gymnospermic eustele from protostelic Devonian ancestors.

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