David raises the question of why dioecious plants don't have more asexual
reproduction. Perhaps they just aren't old enough. In bryophytes,
dioecious plants are more likely to have asexual reproduction than are
monoecious ones. Longton did an interesting study on reproduction and
rarity in British mosses and found:
1. a higher proportion of monoecious than of dioecious species is rare
2. a higher proportion of species not known to produce sporophytes than
species producing them is rare
3. absence of sporophytes is more prevalent among dioecious than
monoecious species
4. a higher proportion of monoecious species producing sporophytes than
of dioecious species is rare
Several recent studies have questioned the evolutionary benefits of
sexual reproduction.
Longton, R. E. 1992. Reproduction and rarity in British mosses. Biol.
Conserv. 59: 89-98.
Janice
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Janice M. Glime, Professor
Department of Biological Sciences
Michigan Technological University
Houghton, MI 49931-1295
jmglime at mtu.edu
906-487-2546
FAX 906-487-3167
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