XVI International Botanical Congess

The present day Pinus occidentalis has a strong assemblage of ectomycorrhizal symbionts present over a range of 850-2430 M and the only ectomycorrhizal host in the 320,000 ha pine forest in the Cordillera Central and Sierra de Bahoraco. The fungi present are associated with 10 species of diploxylon pines present in the Sierra Madre Oriental north to Northeastern, US. A second distibution north in the Sierra Madre Occidentale extends to the Rocky Mt's. The diversity of symbionts on P. occidentalis includes 20 genera and over 60 species closely realted to the eastern species. A few species (eg.Suillus albivelatus)are only known from the western US. Dominant genera are Amanita, Russula, and Cortinarius. Endemic species and the rate of endemism and origins of the symbionts of the pine are discussed.