01878nas a2200157   4500008004100000245012900041210006900170260000900239300001400248490000700262520134300269100001601612700001701628700001701645856005801662       2002                        eng d00aLimited hybridization between Quercus lobata and Quercus douglasii (Fagaceae) in a mixed stand in central coastal California0 aLimited hybridization between Quercus lobata and Quercus douglas  c2002  a1792-17980 v893 aMany oak species are interfertile, and morphological and genetic evidence for hybridization is widespread. Here we use DNA microsatellite markers to characterize hybridization between two closely related oak species in a mixed stand in central coastal California, Quercus lobata (valley oak) and Q. douglasii (blue oak) (Fagaceae). Genotypes from four microsatellite loci indicate that many alleles are shared between the two species. However, each species harbors unique alleles, and allele frequencies differ significantly. A Bayesian analysis of genetic structure in the stand identified two highly differentiated genetic clusters, essentially corresponding to species assignment based on morphology. Data from the four loci were sufficient to assign all 135 trees to one of the two species. In addition, five putative hybrid individuals having intermediate morphologies could be assigned genetically to one or the other species, and all but one had low probability of hybrid ancestry. Overally, only six (4.6%) trees showed >0.05 probability of hybrid ancestry, in all cases their probabilities for nonhybrid ancestry were substantially higher. We conclude that adult hybrids of Q. douglasii x Q. lobata are rare at this site and plasticity in morphological characters may lead to overestimates of hybridization among Quercus species.1 aCraft, K.J.1 aAshley, M.V.1 aKoenig, W.D.  uhttp://www.amjbot.org/cgi/content/abstract/89/11/1792