ESTUDIO FLORÍSTICO DEL PEDREGAL DE ARÓCUTIN, EN LA CUENCA DEL LAGO DE PÁTZCUARO, MICHOACÁN, MÉXICO.

The pedregal of Arócutin, with a surface area of approximately 31 km², is located in the Lake Pátzcuaro basin, in the northern portion of the Mexican state of Michoacán. This region belongs to the Trans-Mexican Volcanic Belt physiographic province. The vegetation found is an oak forest in different stages of succesion, intermixed with elements of tropical deciduous forest. The structure and floristic composition of each association is described. Intense botanical exploration for a period of two years resulted in the collection of 407 species of vascular plants, belonging to 262 genera and 96 families; these represent 38.76% of the total number of species in the Lake Patzcuaro basin. The most diverse families are: Compositae with 60 species, Leguminosae with 27, Labiatae with 19, and Gramineae with 18. Comparing the floristic list of the pedregal of Arócutin with those of three other outcrops of basaltic rocks along the Trans-Mexican Volcanic Belt, using the Sörensen similarity index, we found that the Arócutin and Huaniqueo pedregals are the most closely related, both at generic arid specific level. This is followed by the pedregal of San Ángel in Mexico City and finally the pedregal of Chichinautzin, Morelos. Additionally, traditional uses of some plants are recorded. [ABSTRACT FROM AUTHOR]