Gymnosperms and cladistic biogeography of the Mexican Transition Zone

Distributional patterns of 81 species of three genera of Mexican gymnosperms (Ceratozatnia, Dioon, Pinus) were analvzed to evaluate their contribution to the cladistic biogeography of the Mexican Transition Zone, applying Brooks Parsimony Analysis (BPA) and parsimony analysis of paralogy-free subtrees (PAPS). BPA showed three main groups of areas: clade A is corriprised of the Baja California, Great Basin, and Mojavean provinces; clade B includes the Valle de Tehuac6n-Cuicatl n, Balsas Basin, Planicie Costera del Noreste, Planicie Costera del Niloroeste. Costa del Golfo de M6xico, and Costa Pacifica provinces, located along the coasts and in the central lowlands of Mexico-, arid clade C includes the Appalachian, Atlantic and Gulf Coastal, Yucatan Peninsula, Caribbean, Californian, VanCOLIverian, Eastern Central America, Soconusco, Serranias Transistinicas, Serranias Meridionales, Sierra Madre Occidental, Altiplano, and Sierra Madre Oriental provinces, corresponding to the montane areas of the Mexican Transition Zone, Central America and some areas of the U.S.A. PAPS showed three groups of areas: clade D includes the Vancouverian, Appalachian, arid Atlantic and Gulf Coastal provinces; clade E the Balsas Basin, Planicie Costera del Noreste, and Planicie Costera del Noroeste provinces; arid clade F the Serranfas Transistrnicas, Socoriusco, Serranias Meridionales, Sierra Madre Occidental, Altiplano, Sierra Madre Oriental, Baja California, Californian, Great Basin and Mcjavean provinces. Comparing both analyses, three common area relationships ernerge: (1) Appalachian and Atlantic and Gulf Coastal provinces, (2) Great Basin, 'Mojavean and Baja California provinces, and (3) Altiplano, Sierra Madre Oriental and Sierra Madre Occidental provinces. Differences between the general area cladograms can be accounted for by dispersal having a stronger influence in BPA, and the PAPS general area cladograrn showing a clearer vicariant signal. The aerieral area cladograrns obtained support some area relationships not explained in previous studies, and rriay complement the historical distributional patterns of the biota of the Mexican Transition Zone.