Isozymic and chromosomal evidence for the allotetraploid origin of Gymnocarpium dryopteris (Dryopteridaceae).
A critical examination of isozyme, chromosomal, and morphological characters in subspecies formerly included in Gymnocarpium dryopteris demonstrated that three sexual taxa can be distinguished. We recognize these taxa as distinct species: the widespread, fertile allotetraploid G. dryopteris, with one genome derived from the western diploid G. disjunctum and the other from G. appalachianum sp. nov., a previously undetected eastern North American diploid, which is described and illustrated here and for which we report a chromosome number of 2n = 80. Population comparisons of allele frequencies between C. disjunctum and G. appalachianum yielded an average Nei's genetic identity value (I) of 0.274. A wide-ranging assemblage of putatively triploid plants with both sterile, malformed spores and large, round spores capable of germination is believed to represent the backcrosses G. disjunctum X dryopteris and G. appalachianum X dryopteris. The name G. X brittonianum comb. nov. is applied here to G. disjunctum X dryopteris. A key to fertile species, species descriptions and illustrations, distribution maps, and habitat notes are included.
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