Flora and vegetation of the Tucson Mountains, Pima County, Arizona

Abstract

I compiled the first vascular flora of the Tucson Mountains of southeastern Arizona, part of the Arizona Upland subdivision of the Sonoran Desert. The study area consisted of over 40,000 hectares, with two principal biotic communities: desertscrub and desert-grassland. Over 300 km of trails, ridges, washes, canyons, and peaks were surveyed in a three year period, covering all elevations and habitats. This was supplemented by examination of herbarium records. The area is unusually rich compared to other regional floras in the state of Arizona, including a vascular flora of 605 specific and infraspecific taxa in 331 genera and 80 families. The distribution of life forms is: herbaceous annuals and perennials (73%), shrubs (9%), subshrubs (8%), succulents (4%), and trees (1%). Obligate annuals make up 45% of the flora, of which 62% are obligate spring annuals, 33% obligate summer annuals, and 5% either spring or summer annuals. Historical records from the first part of the century are reviewed and compared with the present day flora; 27 species that were found in the Tucson Mountains prior to 1950 have not been collected since, in spite of increased sampling effort. A disproportionate number of these locally-extirpated species are winter annuals.