SPERMATOZOIDS OF MICROCYCAS-CALOCOMA - ULTRASTRUCTURE

Microcycas calocoma, a monotypic Cuban endemic cycad, differs from other cycads in possessing multiple spermatozoids (up to 16 per pollen tube, in comparison with the usual two). The spermatozoids are characterized further by exhibiting a development gradient in complexity and motility, ranging from well-organized and actively motile first-formed spermatozoids to less well-organized and less and less motile last-formed spermatozoids. It is thought that this relationship exemplifies evolutionary reduction and represents a primitive stage in male-gamete evolution and that Microcycas, therefore, is the most primitive member of the Zamiaceae.