The genus Astragalus (Leguminosae: Papilionoideae: Galegeae) in Mexico

Astragalus is the most diverse genus within flowering plants with almost 2500 species, it is widely distributed around the world, very abundant in temperate regions of the Northern Hemisphere, in central and western Asia, Turkey, Iran, and Afghanistan, central Asia, Europe, Mongolia, Siberia, northeastern China, and Japan. In the American continent it is especially abundant in Canada, western United States, Mexico, and South America.

Given the diversity of Astragalus species present in Mexico, the recent description of at least 15 new species for this country, the absence of a recent study that encompasses all the new findings and that the last general study for Mexico dates back almost 60 years, we consider necessary a new taxonomic synopsis that encompasses all the new information, which is presented here. The study records 102 species of Astragalus in Mexico.

This work is based essentially on the review of collections of specimen samples, type specimens in national and foreign herbaria, data bases, and the collection of specimens of this genus by the authors in the last 40 years and that covers practically the entire area where this genus is distributed in Mexico. In this study we recorded 102 species and 46 infraspecific taxa; seventy one species and 17 varieties are endemic to Mexico.

Baja California (32), Chihuahua (25), Durango (23), Sonora (22), Coahuila (20), San Luis Potosí (17), Nuevo León (17), and Zacatecas (15) are the states with the greatest species richness. In Mexico, the diversity of Astragalus species decreases from north to south and from west to east. Most of the species of Astragalus in Mexico are distributed in the mountains, followed by low and arid plains, including coastal dunes, those last ones, exclusively of the northwestern region.

There are no records of any Astragalus species in Campeche, Tabasco, Quintana Roo or Yucatan. The dichotomous keys are based mainly on the color of flowers, the shape of the pod and if the fruit is sessile or stipitate. For each species is included also a morphological description, habitat, altitudinal range, and distribution map.