Phenotypic variation in Larix lyallii and relations in the larch genus

Abstract

Larix Iyallii Parl, (alpine larch) is a small to medium tree restricted to the timberline zone of the mountainous regions of the Pacific Northwest of the United States and the adjacent southwest of Canada. To examine the pattern of phenotypic variation expressed in alpine larch cones and needles, field collections were made in 1985 and 1986 from 11 populations covering most of the species' range. Additionally, samples were collected from 6 populations of L. occidentalis Nutt, (western larch) to compare these two closely related species. Morphometric analyses were based on 45 needle and 11 cone characters. Alpine larch cones averaged 32.2 mm in length, 14.8 mm in diameter and possessed close to 50 cone scales. Short shoot needles were 26.0 mm long, 0.7 mm wide and 0.5 mm thick. An average of 7.8 epithelial cells surrounded each of the two resin canals In the needles. Both principal component analysis (PCA) and discriminant analysis (DA) distinguished the two species. PCA of the alpine larch needle data indicated limited differentiation between populations. The principal components could not be correlated to latitude, longitude or elevation. DA variation expressed in the needle and cone characters was difficult to interpret: neighbouring populations were often more distinct than distant ones. Microgeographic variation in site and climate may influence alpine larch populations to such an extent that broad geographic patterns, if present, were not detectable. Alternatively, genetic drift may be responsible for the variation displayed. Overall, phenotypic variation within L. Iyallli appears to be less than that observed In L. occldentalis. The general methodology used to examine alpine and western larch populations was applied to herbarium specimens made from the living collection of larches of the Arnold Arboretum of Harvard University, representing 7 of the 10 recognized species of Larix Mill. Based on the limited number of samples available, DA correctly classified all specimens Into their correct species groups. The expressed pattern of variation was loosely associated with the geographic distribution of the species. DA, and PCA, also distinguished, and thus provided some support for, the two proposed sections of Larix. Multiserlales Patschke and Pauciseriales Patschke.