Studies on the genus Apios. I. Chromosome number and distribution of Apios americana and A. priceana

Two sonatic chromosome numbers were found for the leguminous plant Apios americana Medikus, i.e., 22 and 33. The former was interpreted as diploid, and the latter, as triploid. The triploid form predominated in the northern range of the species. The diploid was represented in northern material by a single collection (from Medoc, Ontario). A collection of plants produced from seeds obtained from a site in Tennessee was uniformly diploid. A combination of triploidy and self-incompatibility is suggested as the cause of the apparent complete sterility of the species over much of its range. Characterization of individual clones indicated that at least three different triploids were in existence. One of these was distributed over much of the northern range of the species. Chromosome counts of Apios priceana Robinson, a rare and the only other known American species in the genus, showed it to be a diploid with 22 somatic chromosomes.