We compared genetic diversity estimated from allozymes and from random amplified polymorphic DNA (RAPDs) in a sample of 210 Great Basin bristlecone pines (Pinus longaeva Bailey) from three groves in the White Mountains, California, USA. The White Mountains are the most westerly extension of bristlecone pine and home to the oldest known living trees. We assayed two forks of each tree to determine whether they originated from multiple seed caches of the Clark's nutcracker. Despite the limited and fragmented distribution of bristlecone pine, its level of genetic diversity was comparable to that of other pines, but lower than that reported for eastern populations of Great Basin bristlecone pine. Twenty-six of 36 allozymes were polymorphic (p(95) = 38.9%; p = 63.0%), with observed heterozygosity (H(o)) of 0.122 and expected heterozygosity (H(e)) of 0.134. The proportion of the total variation among populations (G(ST)) was only 0.011. The high proportion of trees with multiple stems was not due to germination in seed caches; only six of 210 forked trees had multiple allozyme genotypes. Of the 42 RAPD loci scored, 27 were monomorphic. Genetic diversity for RAPDs was nearly the same as that for allozymes (p(95) = 34.1%, H(e) = 0.130). However, the estimates of diversity and differentiation were much higher (H(e) = 0.321, G(ST) = 0.039) after excluding monomorphic loci.

-Rare plant species are commonly hypothesized to have little genetic variation because of genetic drift, strong and directional selection toward genetic uniformity in a limited number of environments, inbreeding depression and/or other factors. We investigated genetic variation in Berchemia berchemiafolia, a rare and endangered tree species worldwide, by examining 14 allozyme loci and 28 I-SSR amplicons in 111 individuals distributed among four populations in Korea. No allozyme and I-SSR variation were detected with the exception of one variant from one individual at Pgi-2 locus. A substantial genetic bottleneck accompanying the fluctuation of local population size caused by repeated human activities and inbreeding could account for this species' lack of genetic variation. Berchemia berchemiaefolia

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