sentences:  The Tehuacán Valley matorral is bounded by the Trans-Mexican Volcanic Belt pine-oak forests to the northwest, north, and northeast, the Sierra Madre de Oaxaca pine-oak forests to the east, and by the Balsas dry forests to the southeast, south, and southwest.The Tehuacán Valley matorral is a center of plant diversity, with over 2700 species, of which approximately 30% are endemic.It is a center of diversity for species of "Agave", "Hechtia", "Salvia", and cactus.