Chihuahuan Desert Flora of La Calera, Municipio de Agua Prieta, Sonora, Mexico

A total of 555 plant collections were made on 20 trips in 2002-2008 to La Calera area in the Sierra Anibácachi, Municipio de Agua Prieta, 11.3 km south of the Arizona border (31°13’59”N 109°37’53”W, elevation range from 1220 m to 1539 m) in northeastern Sonora. Chihuahuan desertscrub on limestone substrates is dominated by creosotebush (Larea divaricata), Chihuahuan whitethorn (Acacia neovernicosa), mariola (Parthenium incanum), and tarbush (Flourensia cernua). Riparian vegetation along a rocky bedrock/ gravel wash includes desert willow (Chilopsis linearis), netleaf hackberry (Celtis reticulata), desert hackberry (C. pallida), woolly buckthorn (Sideroxylon lanuginosum), soaptree yucca (Yucca elata), Arizona walnut (Juglans major), and Coahuila juniper (Juniperus coahuilensis). The flora is diverse with 350 taxa in 60 families and 222 genera in 25 km2 (2.5 km2 extensively inventoried). Only 5.1% of the taxa are non-native. The most numerous plants are in the Poaceae (57 taxa), Asteraceae (53), Fabaceae (26), Malvaceae (22), and Euphorbiaceae (21) in the genera Euphorbia (11), Abutilon and Bouteloua (7 each), Eragrostis and Muhlenbergia (6 each), and Dalea, Ipomoea, and Sphaeralcea (5 each). Twenty-six taxa are probably the first records for Sonora. Another 21 taxa are noteworthy state records (rare or significant range extensions).