Flora

Transects were done in desertscrub on limestone to characterize the flora of the westernmost Chihuahuan Desert. Most of the sites (15) were in the Municipios of Agua Prieta and Naco in northeastern Sonora, with single sites near Ascensión, northwestern Chihuahua and east of Douglas in southeastern Arizona. A total of 236 taxa were recorded on transects. Dicot perennial herbs (66 species) were the most numerous life forms, followed by annual herbs (36 species), subshrubs (36 species), and woody shrubs (33 species).

Ejido Tonibabi is located 12 kilometers east-northeast of Moctezuma in east-central Sonora, México (29°50’16’’N 109°33’45’’W, 780 m elevation). The vegetation is riparian in the wetlands and foothills thornscrub on slopes. The flora was inventoried on transects in different areas in Ejido Tonibabi. Specimens were collected to identify by comparing with specimens in the University of Arizona and Universidad de Sonora Herbaria and for voucher specimens. A total of 162 species in 125 genera and 47 families were documented in the area.

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).

This flora of the vascular plants of the Tinajas altas region, within the Lower colorado valley subdivision of the Sonoran desert of southwestern arizona, includes the present-day species as well as fossils recovered from packrat middens. The vegetation and flora are dynamic, changing even now, and have changed dramatically during the past millennia, along with shifting climate and human presences.