This magnificent flora of the Sonoran Desert’s southern edge represents decades of meticulous work and the genius of Richard Felger (1934–2020) and his colleagues at their best. It is many things at once.
Thirty-eight plant taxa are reported for Sonora, Mexico, for the first time. Specimens, observations, and images are deposited in herbaria and are available in the SEINet online databases.
The flora of the lower Río Bavispe Valley from the Huásabas area south to the Río Áros at 430 to 1,510 m. elevations (1,410 to 4,954 ft.) was studied from 1995 to 2016. A total of 401 plant taxa in 74 families and 274 genera were recorded in the lower Río Bavispe Valley study area, including 24 non-native species (6.0%). The families with the most species were Asteraceae (50), Fabaceae (50), Poaceae (42), Euphorbiaceae (20), Malvaceae (19), Cactaceae (13), Solanaceae (15), and Pteridaceae (11), representing 54.9% of the flora.
The Municipio de Yécora is in the Tropical Madrean zone of the Sierra Madre Occidental in eastern Sonora, Mexico. The flora is very diverse with 1777 taxa in 150 families and 687 genera. The most important families and genera are Asteraceae (14.5% of the flora), Poaceae (11.3%), and Fabaceae (10.6%), Muhlenbergia (38 taxa), Euphorbia (31 taxa), Cyperus (29 taxa), Ipomoea (26 taxa), Quercus (23 taxa including 7 hybrids), and Dalea (22 taxa). Herbaceous plants dominate the flora (71.3%).
An introduction is provided for the modern and fossil vascular plant flora of the contiguous protected areas of Organ Pipe Cactus National Monument, Cabeza Prieta National Wildlife Refuge, and the Tinajas Altas Region in southwestern Arizona—the heart of the Sonoran Desert. These three entities encompass 514,242 hectares (1,270,700 acres), approximately 5141 km (1985 mi ). Elevation and ecological diversity generally decreases from east (Organ Pipe) to west (Tinajas Altas) while aridity increases from east to west, both correlating with decreasing botanical diversity.
Cañón del Nacapule cuts into the southeastern flank of the Sierra El Aguaje, a rugged volcanic range about 20 kilometers northwest of Guaymas. Nacapule is included in the Sonoran segment of the Gulf Coast subdivision of the Sonoran Desert. The bi-seasonal (summer and winter) rainfall is highly variable. Many plants of tropical origin reach their northern limits in this region or do not extend farther north in the arid coastal desert of western Sonora.
The floras of the tropical vegetation in the Sky Island Sierra la Madera (SMA) near Moctezuma in northeastern Sonora (30°00’N 109°18’W) and the Yécora (YEC) area in the Sierra Madre Occidental (SMO) in eastern Sonora (28°25’N 109°15”W) were compared. The areas are 175 km apart. Tropical vegetation includes foothills thornscrub (FTS) in both areas and tropical deciduous forest (TDF) in the Yécora area. A total of 893 vascular plant taxa are known from these areas with 433 taxa in FTS and 793 in TDF.
The Sierra Bacadéhuachi in east-central Sonora is the westernmost mountain range in the Sierra Madre Occidental (SMO), located east of Bacadéhuachi, Municipio de Bacadéhuachi, 34 km east of the Chihuahua border, and 165 km south of the Arizona border. The vegetation ranges from lowland foothills thornscrub up through desert grassland to oak woodland and pine-oak forest. The flora was sampled in December 1995, July 2008, June, August, and September 2011, and March 2012. The flora totals 442 taxa in 297 genera and 96 families.
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).
