SYSTEMATICS OF MIELICHHOFERIA (BRYACEAE, MUSCI) .3. HYBRIDIZATION BETWEEN M-ELONGATA AND M-MIELICHHOFERIANA

Allozyme variation in mixed populations of Mielichhoferia elongata and M. mielichhoferiana was investigated to determine if interspecific hy bridization occurs when these two closely related species grow togethe r. Previous research has shown that M. elongata and M. mielichhoferian a can be distinguished by three diagnostic isozyme loci (Gpi-1, Mdh-2, and Mdh-3) at which the two species do not share alleles in 32 allopa tric populations from North America and Europe. The present study show s that in five populations from Colorado, Norway, and Sweden, gametoph ytes resulting from interspecific hybridization can be recognized by r ecombinant genotypes combining alleles of the otherwise diagnostic loc i. A total of 32 multilocus genotypes was found among the 111 individu als sampled, of which 13 were recombinants. The frequency of recombina nts ranged from 12% to 35% within populations, and all but one populat ion contained both parental species. Moreover, recombinant genotypes c ould be accounted for by the allelic constitution of sympatric parents . In two of the populations, more than one hybridization event was nec essary to account for the diversity of recombinant genotypes. Twenty-n ine of the 32 genotypes detected in this study were restricted to one population each, two occurred in two Swedish populations separated by approximately 14 km, and one occurred in both Sweden and Norway.