Allozymes were used to study the spatial attributes of clones (genets) comprising a population of Pteridium aquilinum (L.) Kuhn var. latiusculum (Desv.) Underw. ex Heller (bracken fern) in the Appalachian Mountains of Virginia. Ramets (individual leaves) were sampled at intervals of 165 m (or less in some cases) and genotyped for six polymorphic isozyme loci to produce a map depicting the spatial patterning of genets. Forty-five distinct genotypes were detected, 14 of which were sampled more than once, five of these more than four times. Genotype proportions at all loci except Pgm-1 conformed to Hardy-Weinberg expectations. Estimation of allele frequencies in the population used a "round-robin" approach that removed any upward bias for rare alleles that distinguish genets. Based on these allele frequencies, the probability that each genotype could arise independently and be sampled was calculated. Some genotypes represented by widely separated ramets had very low probabilities of re-encounter, documenting fragmentation of widespread genets. Coarse-scale mapping indicated a population consisting of many small genets and a few very large ones (up to 1,015 m across). The larger genets tended to be irregular in shape, fragmented, and overlapping. Fine scale mapping of individual fronds in spatially discrete patches of ramets revealed extensive intergrowth of genets, indicating that P. aquilinum exhibits a "guerrilla-type" clonal morphology.

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A large proportion of plant species has originated through allopolyploidy: interspecific hybridization followed by chromosome doubling. Heterozygosity remains fixed in allopolyploids because of nonsegregation of parental chromosomes. Two allotetraploid species of the fern genus Asplenium show allozyme polymorphisms at loci that are polymorphic in their diploid progenitors, indicating that each has originated more than once and implicating continued gene flow from diploids to tetraploids.