Application of parsimony analysis of endemicity to Mexican gymnosperm distributions: gridcells, biogeographical provinces and track analysis

Parsimony analysis of endemicity (PAE) was used to analyse the distributional patterns of 124 species of Mexican gymnosperms, using two different sample units: gridcells and biogeographical provinces. PAE analyses were based on distributional data from herbarium specimens and specialized literature. Two data matrices were constructed for 60 gridcells of 2 degrees and 14 biogeographical provinces. The analysis of the 2 degrees gridcell matrix led to 7084 cladograms. The strict consensus cladogram showed several clades equivalent to the results obtained with the biogeographical provinces. Three clades agree with some principal regions of distribution of Mexican pines, previously identified by several authors, located at the northern portion of the Baja California peninsula, the Sierra Madre Occidental, and the Sierra Madre Oriental. These areas represent important centres of species diversity and endemism for Mexican gymnosperms. The analysis of the province matrix led to two most parsimonious cladograms, which only differed in the position of the Sierra Madre Occidental province. The iterative procedure PAE with progressive character elimination was applied to identify generalized tracks, where clades of provinces were considered equivalent to generalized tracks, and each time a cladogram was obtained, species defining its clades were deleted and a new run was undertaken. We found five generalized tracks, mainly located in montane provinces. The distribution patterns of gymnosperms agree with the existence of several Mexican biogeographical provinces, and a different historical biogeography of the Mexican peninsulas from the rest of the country is evident