Geographical and ecological distribution of Ipomoea (Convolvulaceae) in Michoacan State, Mexico

Of the 2 663 genera of vascular plants in Mexico, Ipomoea (Convolvulaceae) ranks 10th in number of species, and it is the most speciose genus in Michoacan. With 75 species recorded from the state. Michoacan contains approximately 44% of the species reported from Mexico, this despite that the state represents only 3% of the country's surface area. We studied the geografic distribution and the relation between species richness and environmental factors within Michoacan. Through the examination of the major Mexican herbaria, as well as field exploration, we obtained 553 georeferenced specimens. The state was divided into 15 km(2) quadrants in order accommodate the collections, and a map was produced to demonstrate species richness. The relation between species richness and altitude, precipitation, temperature, soil, and vegetation type was explored. Northeastern Michoacan had the greatest number of specimens, as well as the highest species richness. On the contrary, the southwestern portion of the state had the fewest specimens, but also had high species richness. With respect to mean temperature and precipitation, the greatest number of species was found to occur between 15 to 30 degrees C and 899 to 1 199 mm, respectively. The altitudinal gradient of the distribution was bimodal, with one peak between 0 to 299 m and another between 1 800 and 2 099 m. A preference was found for tropical deciduous forest and secondary grasslands, as well as for litosol, vertisol, and luvisol soils.