MACROMORPHOLOGICAL ANALYSIS AND CYTOGENETICS OF THE GENUS COSMOS (ASTERACEAE, COREOPSIDEAE), WITH A KEY FOR ITS IDENTIFICATION

The genus Cosmos is restricted to the Americas, and Mexico represents its center of diversification. Some species have a wide distribution and have been intensively collected, whereas others, due to their narrow distribution, are poorly known. This has generated a poor understanding of its morphological variability and infrageneric and interspecific limits, as well as confusion at the intergeneric level within tribe Coreopsideae. Polyploidy and aneuploidy have played an important role in the speciation of the group. The ploidy level variation can be seen between species, as well as in populations of the same species. Macromorphological data are used to support recognition of intergeneric limits, infrageneric groups, and species. Evidence of chromosome number variability and geographic distribution information for Cosmos is also included. These data are fundamental for the taxonomic understanding of the genus. A key for the identification of all species of Cosmos is provided.