Sex expression, population structure, and floral dimorphism in a gynodioecious herb, Agastache rugosa (Lamiaceae) in Korea

We investigated phenotypic expression and floral dimorphism in Agastache rugosa, a gynodioecious perennial herb, in five Korean populations. Three phenotypes, based on their reproductive characteristics, were found: plants with hermaphrodite flowers (male fertile); plants with female flowers (male sterile); and an intermediate phenotype, which had both hermaphrodite and female flowers within the same inflorescence. Most populations consisted of hermaphrodite and female individuals, together with the intermediate phenotype. Floral dimorphisms were found in nearly all the organs studied, including the corolla, calyx, and stamen, but not between the gynoecium of hermaphrodite and female flowers. Hermaphrodite flowers always had larger floral parts than those of the female and intermediate phenotype. Although there were no significant nutlet size differences between sexual types, nutlet weight was consistently greater in females than in hermaphrodites. Hermaphrodite flowers possessed a high proportion of fertile pollen grains, whereas in the intermediate phenotype, there was either the same amount of sterile and fertile grains or there were more sterile than fertile grains. The differences in the quality and quantity of pollen grains between the hermaphrodite and intermediate phenotype may reflect a trade-off between male and female function. These results indicate that intermediate flowers may be a transitional sexual morph toward female flowers. (C) 2015 Elsevier GmbH. All rights reserved.