Electrophoretic Evidence for the Origin of Fern Species by Unreduced Spores

Allopolyploid speciation is well documented in the ferns, but data from enzyme electrophoresis have only recently shown that certain sexual and agamosporous taxa are autopolyploids. Autopolyploidy may arise through fertilization involving gametophytes from unreduced spores, a mechanism previously proposed to account for the origin of allopolyploid Asplenium plenum. This report assesses the ability of unreduced spores to function in the origin of polyploid fern species by using enzyme electrophoresis to test their hypothesized role in the origin of A. plenum. Six isozymes of the enzymes PGI, PGM, TPI, 6PGD, and LAP are species‐specific for the taxa proposed as parental under two competing hypotheses for the origin of this species. Electrophoretic data reject the more conventional hypothesis involving simple hybridization and agree perfectly with expectations under the more complex hypothesized origin via unreduced spores. The mechanism whereby unreduced spores have functioned in this case is no different from that by which they would function in the origin of autopolyploid taxa and may be more common in the origin of fern species than previously suspected.