An electrophoretic study of representatives of subgenus Diploxylon of Pinus

Abstract

Relationships among 14 taxa in subgenus Diploxylon of Pinus from Mexico and the United States were analyzed using 15 isozyme loci obtained from both frozen and fresh needle tissue. The phenogram obtained from cluster analysis of genetic distance values and phylogenetic trees implementing the distance Wagner procedure were in general agreement with classifications based on morphological features. Pinus leiophylla is genetically distinct from other species. Two groupings, one comprising P. oocarpa and P. pringlei and another comprising P. lawsonii and P. teocote, correspond to sections Serotinus and Teocote (sensu Martínez), respectively. Classification of the remaining eight taxa has varied, ranging from their placement in three, two, or only one section. Isozyme analysis resulted in a group that included P. cooperi, P. douglasiana, P. durangensis, P. michoacana, and P. montezumae, which suggests genetic affinity between Sections Pseudostrobus and Montezumae (sensu Martínez). This result corresponds more closely to the placement of these species in subsection Pseudostrobi. The distant relationship between P. engelmannii and the ponderosa pines may be anomalous (an artifact of small sample size) or may indicate greater genetic divergence than previously recognized.