Leaf morphometric variation in Quercus affinis and Q-laurina (Fagaceae), two hybridizing Mexican red oaks

Leaf variation was examined in two hybridizing Mexican red oaks, Quercus affinis and Q. laurina. Data of nine traits were obtained for ten randomly chosen leaves in each of 512 individuals from 16 populations sampled along a geographical gradient, including the distribution area of both species and a putative area of secondary contact and hybridization. A cluster analysis recognized two main groups of populations, which were congruent with the taxonomic assignment of the predominant morphological type within the populations and were thus labelled `Q. affinislike' and `Q. laurina-like' population groups. A nested analysis of variance revealed that the largest proportion of the total variation was contained within populations, as among-tree variation (28-54%, depending on the trait), and as intra-individual variation (17-56%). However, differences between the two groups of populations (3-27%) and among populations within groups (5-21%) were also significant for the nine traits. A distinct pattern of change across populations was observed for each trait. Variation was particularly pronounced along the geographical gradient for petiole length and leaf-margin teeth number, possibly implying selection on these two traits. Results suggest that phenotypic plasticity, gene flow, hybridization and natural selection have shaped foliar variation in this oak complex. (c) 2005 The Linnean Society of London, Botanical Journal of the Linnean Society.