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RAPD technique using haploid DNA from megagametophyte tissue was applied to detect the pattern of genetic variation within Abies nebrodensis, a species endemic to Sicily. Results were compared with a reference system composed of representatives of five Mediterranean firs: A. alba, A. cephalonica, A. nordmanniana, A. numidica, and A. pinsapo. Diploid genotypes for RAPD loci were inferred from segregation patterns in haploid megagametophytes from individual trees. Therefore, it was possible to distinguish between homo- and heterozygotes carrying a RAPD fragment and to calculate unbiased estimates of genetic parameters. In the interspecific comparison, A. nebrodensis appears intermixed with the other Abies species, supporting the hypothesis of remarkable hybridization processes within the genus. A high level of polymorphism and deviation from panmictic equilibrium as a result of heterozygote excess depict a pattern of population structure in A. nebrodensis that agrees with the expectations for an outcrossing perennial species, in spite of its critical conditions. Implications with respect to the conservation management of the species are also discussed. [ABSTRACT FROM AUTHOR]