Abstract
Structural members within the exospore ofSelaginella galeottii suggestive of those present at maturity are first detectable when the exospore is approximately 5 µm in thickness. Subsequent changes in successively larger sporangia involve a gradual size increase of the component units simultaneously throughout the exospore. Concomitantly, non-membrane bound material present at the inner surface of the tapetum (and the persistent megasporocytes) and throughout the sporangium locule changes from primarily droplets and weftlike material (including beaded wefts) to coarse fibrous material. The taxa which possess this unusual wall pattern cut across presently accepted taxonomic schemes. This is not the case with the other wall ultrastructural types in the genus. The possibility exists that this megaspore wall type defines a separate lineage within the genus which, by virtue of its large megaspores, was able to compete well and radiate to produce a variety of life forms.
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Taylor, W.A. Ultrastructural analysis of sporoderm development in megaspores ofSelaginella galeottii (Lycophyta). Pl Syst Evol 174, 171–182 (1991). https://doi.org/10.1007/BF00940338
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DOI: https://doi.org/10.1007/BF00940338