PHYLOGENY AND BIOGEOGRAPHY OF THE PINYON PINES (PINUS SUBSECT, CEMBROIDES)

Discrete qualitative and continuous quantitative characters ("gap-coded") are used in a parsimony analysis of the phylogenetic relationships of the pinyon pines. Cladograms constructed using all the data (both discrete and continuous characters) are congruent with those constructed with the continuous characters deleted from the data set. The continuous characters add resolution to clades not resolved by discrete qualitative characters. The resulting phylogeny is then used to examine Axelrod's hypothesis that a Late Tertiary shift in regional climate-the elimination of summer rains in the far western United States-affected the evolution of the regional flora. The cladograms produced by this study are in agreement with the inferred climate changes, with the most recently derived pinyon taxa being those from regions of summer drought. The phylogeny is also used to examine other biogeographic trends, such as a shift towards wider substrate tolerance, and patterns in character evolution, such as the evolution of fewer needles per fascicle in the taxa endemic to areas of summer drought.