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The Coal-Age Flora of Kansas. II. On the Relationships Among the Genera Etapteris, Scleropteris and Botrychioxylon

Robert W. Baxter
American Journal of Botany
Vol. 39, No. 4 (Apr., 1952), pp. 263-274
Stable URL: http://www.jstor.org/stable/2438536
Page Count: 12
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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.
The Coal-Age Flora of Kansas. II. On the Relationships Among the Genera Etapteris, Scleropteris and Botrychioxylon
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Abstract

The stem, Scleropteris illinoiensis, described by Andrews is shown to be congeneric with Scott's Botrychioxylon paradoxum and to possess Etapteris petioles. In view of this fact, both Scleropteris and Botrychioxylon are reduced to species within the older genus Zygopteris. This change in nomenclature is in accord with the suggestion of Sahni that the proven connection of Etapteris with Botrychioxylon would demonstrate beyond doubt the generic identity of Zygopteris and Botrychioxylon. The petiole is described from the point of origin of its vascular strand in the stem stele to the point within the free petiole where it assumes the characteristic configuration of the Etapteris type bundle. Branching of the petiole vascular tissue is illustrated and discussed. The evidence suggests that the so-called secondary and tertiary pinnae have been reduced to photosynthetic aphlebiae. The aphlebiae on the stem are shown to be identical in structure with those on the petioles and it is suggested that the former may represent reduced primary pinnae. The organ genus, Etapteris, is maintained, because although the E. scotti type appears to be borne by Zygopteris stems, the E. diupsilon type exhibits important distinctions in pitting and behavior of the pinnae traces. The structure of the "secondary" wood of the Zygopteris stems is examined and the conclusion is reached that it is actually primary in nature.

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