In vitro hybridisation of Isoetes

W. Carl Taylor, Phyllis G. Reimer
1985 Proceedings of the Royal Society of Edinburgh Section B Biological Sciences  
Species of Isoetes from northeastern North America are sometimes difficult to identify because their diagnostic characters intergrade. It is hypothesised that interspecific hybridisation, which obscures species distinctions, is responsible for this intergradation. To test this hypothesis, experimental crosses were made with spores in culture. Results indicate that spores of aquatic species of Isoetes in northeastern North America are easily germinated in sterile, demineralised water and crosses
more » ... d water and crosses are readily made. Large, easily removable microsporangia and megasporangia facilitate the segregation of male and female gametes. It was also found that vernalisation of spores is important for spore germination or sporophyte formation in some species. Further, among the various taxa cultured, megagametophytes differ in archegonium and rhizoid development. Suspected hybrid taxa produce polymorphic megaspores that vary in size, shape, and surface ornamentation. Less than 1% of these polymorphic megaspores germinate in culture, while normal-looking, uniform megaspores from most species approach 100% germination within 50 days. Megagametophytes which do develop from polymorphic spores bear abnormal archegonia or no archegonia. Species of Isoetes can be crossed in the laboratory, but it appears that hybrid sterility, indicated by the production of polymorphic, non-viable spores, isolates species in nature.
doi:10.1017/s0269727000008721 fatcat:hijhz36ztvaxnitc2ub4pxfluu