Natural poplar hybrids from southern Alberta. I. Continuous variation for foliar characteristics

Abstract

Shoot cuttings were collected from 56 poplars naturally occurring in riparian sites in southern Alberta and southeastern British Columbia and rooted in a greenhouse. Subsequently, the clones were established in a nursery plot at Lethbridge, Alta., and after two growing seasons, fully expanded late leaves from long shoots were collected. Leaf blade lengths, maximum blade widths, petiole lengths, distance from the petiole to the position of maximum width, tip angle from the midrib, margin teeth number, teeth depth, and leaf areas were measured. Petiole length, blade width, teeth number, and blade length were the most heavily weighted factors in a principal-components analysis of these leaf data. No clear disjunction was apparent from the principal-components analysis, which grouped Populus deltoides, P. balsamifera, and P. angustifolia leaf types in different regions of a two-dimensional plot. Continuous variation was observed for the hybrid leaf forms that were intermediate between the parental forms. This continuous variation for Populus leaf form indicates that the three species interbreed freely in southern Alberta, producing a single, dissectional, trispecific, hybrid swarm.