DIFFERENT DEVELOPMENTAL PROCESSES UNDERLIE SIMILAR SPERMATOZOID ARCHITECTURE IN MOSSES, LIVERWORTS AND HORNWORTS

Abstract

  Analysis of the major developmental processes involved in spermatogenesis in bryophytes reveals that the streamlined form of the mature spermatozoids of mosses, hepatics and hornworts is a remarkable example or convergent or parallel evolution, probably consequent on the extreme selective pressures operating on motile cells in the terrestrial environment. Further considerations indicate Lycopodium and Selaginella and members of the Characeae exhibit similar examples of the evolution of comparable, highly specialized male gamete architecture. Recognition that the spermatozoids of mosses, hepatics and liverworts are analogous in structure strengthens the idea that bryophytes are polyphyletic. The morphology of mature spermatozoids, previously considered of major importance in charting interrelationships between major groups of chlolophyll a- and b-containing plants, is meaningless without an understanding of developmental processes.