Allozyme studies of Botrychium have revealed several surprising and seemingly contradictory facts: 1) diploid species have remarkably low genetic variability, and 2) heterozygous individuals within populations are extremely rare, but 3) genetic differentiation between species is high, equaling that between species of most fern genera. Low genetic variability in species and lack of heterozygotes most likely result from sexual reproduction via intragametophytic selfing that is promoted by the underground habitat of the bisexual gametophytes. If this has always been true of Botrychium, then how did inbreeding ancestors with low genetic variability generate the variation to produce the current well-differentiated species. The expected continuous variation among progeny of such species over time must have been recently fragmented into precursors of today's species. Habitat fragmentation by Pleistocene glaciation in the high latitude/high elevation habitats typical of Botrychium is a likely cause of recent speciation events. In Botrychium subgenus Botrychium allotetraploid species outnumber diploids nearly 2 to 1, and many are widespread and considerably more variable genetically and morphologically than their diploid parents. Allotetraploids may be favored because of their greater variability inherited through multiple origins and enhanced through differential gene silencing.

Key words: allopolyploid, Botrychium, gene silencing, self fertilization, speciation