Relationships among Caladium Species: New Insights from Cytological and Molecular Marker Analyses

The genus Caladium is a member of the Araceae family, and several of its species are cultivated as ornamentals. The exact number of species and the relationship among its species need to be better defined. In recent years, we conducted cytological and molecular marker analysis of caladium species accessions that were collected from South and Central America by the Marie Selby Botanical Gardens, and detected a wide range of genome size and chromosome number variation in these accessions. Caladium genome size ranged from 2.98 pg/2C to 9.89 pg/2C and seemed to fall into two groups. Large caladium genomes appear to be duplicated from small genomes. Seven chromosome numbers, 2n = 18, 20, 24, 26, 30, 34, and 38, were observed in these accessions. Molecular marker analysis based on simple sequence repeats further revealed the genetic relatedness of caladium accessions at the molecular level. Our research results suggest a close relationship among Caladium ×hortulanum, Caladium bicolor, and Caladium schomburgkii, support the species status of Caladium humboldtii and Caladium picturatum, and support the new species status of Caladium clavatum. Caladium marmoratum, Caladium praetermissum and Caladium steudneriifolium showed different chromosome numbers and could be considered as distinct species, yet they could be misidentified when solely based on plant morphology. Our studies also suggest that genome duplication, chromosome loss or addition, and chromosome rearrangements might have played very important roles in the evolution of Caladium.