• Desert Plants, Volume 30, Number 2 (January 2015)

      Wiens, John F.; Van Devender, Thomas R.; Dimmitt, Mark A.; Department of Botany, Arizona-Sonora Desert Museum; University of Arizona Herbarium; Center for Sonoran Desert Studies, Arizona-Sonora Desert Museum (University of Arizona (Tucson, AZ), 2015-01)
      Ironwood Forest National Monument, created in 2000, is located west of Tucson and south of Casa Grande, in Pima and Pinal Counties, south-central Arizona. The boundaries encompass parts or all of eight desert hill and mountain ranges and two valleys. In the flora of 593 taxa, one federally listed endangered plant species, Echinocactus horizonthalonius variety nicholii, occurs within the Monument. Two other plant species common in Mexico, Cathestecum brevifolium and Pisonia capitata, have their only known United States populations in the Monument. Flora plots revealed a wide range in species composition and numbers based on topography and geology. Census plots performed on Carnegiea gigantea, Olneya tesota, Parkinsonia florida, Parkinsonia microphylla, and Prosopis velutina showed populations in most areas of the Monument to be healthy and stable. When compared with floras of nearby sites of similar habitat, the Ironwood Forest National Monument was found to be remarkably rich in species and low in exotic taxa.