COMPARATIVE REPRODUCTIVE BIOLOGY OF HERMAPHRODITIC AND MALE‐STERILE IRIS DOUGLASIANA HERB. (IRIDACEAE)

A comparative study of the reproductive biology of male‐sterile and hermaphroditic plants in a gynodioecious population of Iris douglasiana Herb. (Iridaceae) was conducted at the University of California's Marine Laboratory at Bodega Bay, California, between 1976–1979. Each year of the study, there were 11.1% male‐sterile plants in the population, some of which began blooming at the same time as the earliest blooming hermaphrodites. Male‐sterile flowers made up between 7–21% of the flowers produced during the male‐sterile flowering period. Male‐sterile flowers had smaller sepals and petals than hermaphrodites, there were fewer of them per square meter, and they had fewer pollinated stigmas than did hermaphroditic flowers. In a test to determine pollinator preference, intact hermaphroditic flowers tended to have more pollinated stigmas than did hermaphrodites with their stamens removed or those flowers with shortened sepals made to resemble the smaller male‐sterile flowers. Floral phenology and nectar‐flow patterns were similar in both types of flowers as were the kinds of amino acids and sugar rewards in the nectar. Male‐sterile flowers, however, produced much less nectar per flower. There were no significant differences in the number of ovules per flower or the number of seeds produced per capsule between the two flower types, but the loss of seeds through larval predation was much greater in capsules from hermaphroditic flowers. Early flowering and setting of seed by plants with male‐sterile flowers could give them a reproductive advantage over plants with hermaphroditic flowers which experience higher levels of larval predation later in the growing season.