Phenotypic variation of Chinese aspens and their relationships to similar taxa in Europe and North America

Abstract

Morphological variation of leaves and pubescence of buds and shoots from Chinese aspen taxa (sect. Populus of Populus) were studied and compared with those of North American aspens. Data were analyzed for 648 clones from 19 Provinces of Chinese aspen taxa identified on herbarium specimens as P. bonatii Gomb., P. davidiana Dode, P. rotundifolia Griff. var. bonatii Gomb., P. rotundifolia Griff. var. duclouxiana (Dode) Gomb., and P. tremula L. In addition, data from field collections of intact shoots of 137 clones of P. davidiana (Heilongjiang, Jilin, and Shaanxi Provinces) and from 821 clones of P. tremula from Europe were also analyzed. Leaf morphology of herbarium specimens identified as P. davidiana, the most widely distributed Chinese taxon, varied markedly among populations, especially between northern and southwestern China. Clones of P. davidiana from northern and northwestern China were markedly different from those of the P. rotundifolia complex of southwestern China. However, clones identified as P. davidiana from southwestern China were similar to those of P. rotundifolia in leaf shape, number of teeth, and pubescence; they differed only in leaf size. Striking within- and among-population differences were found for field collections of P. davidiana in northeast China. Buds and seasonally determinate shoots of P. davidiana were glabrous in northeast and north-central China; pubescence increased markedly to the southwest. Buds and shoots of clones of the P. rotundifolia complex and P. tremula were predominantly pubescent. The Eurasian aspen taxa are enormously polymorphic in leaf morphology and pubescence; clinal variation along geographic gradients in China, Japan, and Europe are pronounced. Based on studies to date, we would tend to recognize P. davidiana and P. rotundifolia as races of P. tremula. It may be that in all of Eurasia there is but a single, highly polymorphic species, viz. P. tremula. Key words: aspens, China, Eurasia, Populus, morphology, systematics.