Species richness, geographic distribution and conservation status of the genus Dahlia (Asteraceae) in Mexico

Background and Aims: The genus Dahlia (Asteraceae) is native to the Americas and Mexico is its center of diversification. Dahlia is important in ornamental horticulture, and breeding programs have generated more than 15,000 varieties. Mexico represents the main source of germplasm; therefore, a study of its richness and geographical distribution is essential. The aims of this work were to analyze the species richness, geographical distribution and evaluate the conservation status of Dahlia in Mexico. Methods: A database with 1980 georeferenced observations was elaborated from herbarium specimens, publications and field collections. The information was analyzed using Geographic Information Systems to reveal the estimated species richness by political division, vegetation types, regions, biogeographical provinces, elevational, latitudinal and longitudinal ranges, a grid cell of 33 x 33 km, and Protected Natural Areas. Key results: Dahlia consists of 38 species, all growing in Mexico, 35 are endemic. The genus occurs in 26 states. Hidalgo and Oaxaca have the highest number of species, followed by Guerrero. Jalisco has the most records. Commonly, Dahlia grows in coniferous and oak forest. Its distribution ranges from 24 to 3810 m elevation; however, most species are found between 2000 and 2500 m. High species richness occurs in two areas; the first one is located in the Sierra Madre Oriental including northeastern Queretaro, eastern Guanajuato and southern San Luis Potosi; the second one is in the Sierra Madre del Sur in northwestern Oaxaca. Finally, 23 species grow within the boundaries of a Protected Natural Area, and the Sierra Gorda, state of Queretaro, concentrates the highest species number. Conclusions: The analyses of species richness and distribution showed that the greatest diversity of Dahlia is found in the Mexican Transition Zone, in the Sierra Madre del Sur and the Sierra Madre Oriental provinces.