Desert Plants, Volume 12, Number 2 (December 1996)

Abstract

The Tucson Mountains are a small desert range (about 40,000 hectares) in the Arizona Upland subdivision of the Sonoran Desert in Pima County, southern Arizona. They lie in an ecological transition between the Sonoran Desert and higher biotic communities including desert grassland, chaparral, and montane woodlands and forests. The dominant vegetation types are desertscrub and desert grassland. The vascular flora is unusually rich with 610 species and 23 infraspecific taxa in 334 genera and 80 families. Ten families make up 62 percent of the flora while 29 families are represented by a single species. Life forms include herbs (76 percent), shrubs (nine percent), subshrubs (seven percent), succulents (six percent), and trees (two percent). The herbaceous species are largely represented by grasses (20 percent) and composites (17 percent). Annuals are the most common life form (45 percent). These grow in response to precipitation in the winter-spring (61 percent), summer-fall (33 percent), or both (six percent). Most taxa (51 percent) were found at less than five locales; these locally distributed species are generally rare or uncommon. Thirteen percent of the flora are introduced exotics of which only seven species are well established in undisturbed habitat. Over 3200 specimens have been collected since 1884, providing a rich history for a local flora. Approximately 25 species were collected prior to 1950 that have not been collected since.