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Journal Article

Observations on Ptyxis, Phenology, and Trichomes in the Cycadales and their Systematic Implications

Dennis Wm. Stevenson
American Journal of Botany
Vol. 68, No. 8 (Sep., 1981), pp. 1104-1114
Stable URL: http://www.jstor.org/stable/2442720
Page Count: 11

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Topics: Trichomes, Taxa, Leaves, Hair, Genera, Plant cells, Phenology, Stipules, Botany, Plants
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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.
Observations on Ptyxis, Phenology, and Trichomes in the Cycadales and their Systematic Implications
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Abstract

Ptyxis, phenology, and leaf trichomes are described for 43 species representing all ten genera in the Cycadales. The typical annual growth sequence is: leaf flush production, cataphyll production, reproductive production, and finally cataphyll production in all taxa except Stangeria which does not have cataphylls and produces leaves one at a time throughout the year. The leaf and cataphyll bases are slightly winged except in Zamia and Ceratozamia, which have well developed stipules, and in Stangeria, which has a distinctive adaxial, stipular hood on the leaf bases. Longitudinal ptyxis of the whole leaf is of four types: circinate (only in Bowenia); erect (Cycas, Dioon, Encephalartos, Lepidozamia, Macrozamia, Microcycas, and some Zamia spp.); inflexed (Stangeria, Ceratozamia, and some Zamia spp.); and reflexed (rarely found in Cycas and Dioon). The pinnae are oriented so that the horizontal ptyxis is conduplicate in all taxa except Bowenia and Cycas where it is involute. The individual pinnae are circinate in Bowenia and Cycas, conduplicate in Stangeria, and flat in all other taxa. The pinnules of Bowenia are also flat. Leaf trichomes are of six types: transparent unbranched; transparent branched; colored unbranched; colored branched; colored idioblastic; and short colored curved. Cycas has only transparent branched (unequally) and unbranched. Ceratozamia, Dioon, Encephalartos, and Stangeria have transparent and colored trichomes, both unbranched. Bowenia, Lepidozamia and Macrozamia have short colored curved hairs and transparent unbranched hairs. Macrozamia is the only taxon with colored idioblastic trichomes. Zamia and Microcycas have transparent and colored hairs. Both trichome types occur branched and unbranched. Because of its decompound leaf, circinate ptyxis, cones on short determinate branches and other distinct characters the family Boweniaceae D. Stevenson fam. nov. is described. This family contains one genus: Bowenia.

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