Hybridization of the California Firs

Abstract

Abstract Four groups of firs (sections, in the most recent classification of Abies) are represented in California. Crossing within these sections is possible and even easy, and in two of the sections intergrading populations between highly crossable taxa are wide-spread in California. An exception is A. amabilis, a Northwestern fir that has not been crossed with other species in the same section (Grandes: A. concolor, A. grandis) or in other sections (e.g., Nobiles: A magnifica). Crossing species in different sections is usually difficult or impossible. The genetic isolation of A. bracteata, an endemic species classified as a monotypic subgenus or section, may be nearly complete: two probable hybrids with A. concolor died at a few years of age. A few putative hybrids from intersectional crosses between species in Grandes and Nobiles died within months of germination. Intersectional crosses with firs outside California (two Mexican and four Eurasian species) all failed except A. concolor x A. religiosa, which produced numerous healthy hybrids. The common occurrence of genetic barriers in Abies is at odds with the long-held view that it is easy to hybridize fir species. For. Sci. 34(1):139-151.