Species Crossability in Spruce in Relation to Distribution and Taxonomy

Abstract

The author describes the results of experiments on artificial hybridization of Picea spp. Considering his own results in conjunction with those of other investigators, he refers to 70 different attempted interspecific crosses, exclusive of reciprocals. Combination of data on crossability, geographical distribution and morphological features has led the author to suggest the following hypotheses of the evolution of the genus. Picea had a monophyletic origin and the basic type has undergone relatively little change in the course of speciation. Mutations have occurred at many loci but few allelic series have been established and interactions between genes have remained weak. The genus originated in north-eastern Asia, whence it spread along boreal routes and southwards along mountain chains. The southern species, compared with the northern, have smaller geographical ranges, many of which are decreasing at the present time. Genetic uniformity and specialization for survival in southern habitats, together with a smaller capacity for evolutionary change than the associated competing angiosperms, have contributed to this diminution in range. Barriers to interspecific crossing have arisen mainly from genie differentiation subsequent to speciation due to geographical isolation. Introgression has been observed in certain regions and probably played a significant role in evolution during the past. The species are divided into groups according to their putative relationships.