Allozyme investigation of the isoetes riparia alltetraploid complex



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Texas Tech University


This thesis addresses a systematic problem within Isoetes, a genus comprising approximately 150 species worldwide, 25 of which are currently known from North America. Isoetes is the sole extant genus of Isoetaceae which, along with Lycopodiaceae and Selaginellaceae, are the extant families of Lycopodiophyta, the most primitive division of vascular plants. Isoetes is heterosporous, i.e., producing sexually dimorphic spores, an apomorphic condition shared via convergence with spermatophytes but restricted among pteridophytes to a few taxa. Isoetes microspores (male) are usually less than 50 microns in diameter while megaspores (female) are mostly greater than 300 microns in di£mieter (Taylor et al. 1993).

Isoetes comprises herbaceous perennials with a very simple yet unique form. This uniqueness in form helps to distinguish Isoetes from other kinds of plants, but their simplicity poses difficulty in species identification due to a resultant lack of taxonomic characters. Isoetes plants have a small, lobed, subterranean stem (corm) from which a spiral array of terete to angular quill-like microphylls (leaves) ascend, acheiving lengths of 1 to 100 cm. Each microphyll possesses either a microsporangium or a megasporangium that develops on the adaxial side of the expanded microphyll base. Sporangia are covered to varying degrees by a thin layer of tissue, the velum (Taylor et al. 1993).



Riparian plants, Plant isozymes, Isoenzymes, Plants