Mating Systems and Seed Reproduction in Gynodioecious Geranium asiaticum (Geraniaceae)

Mating systems and seed reproduction in gynodioecious Geranium asiaticum Serg. (G. bifolium Patrin.) were studied in four coenopopulations of Western Siberia (Novosibirsk region). The bisexual flower of hermaphrodite individuals of G. asiaticum is characterized by a longer flowering (2.5-3.5 days) than the pistillate flower of female individuals (2-2.5 days), due to the passage of the male (staminate) phase at the beginning of morphogenesis: G. asiaticum is characterized by strict protandry. Mating of individuals of G. asiaticum occurs according to the type of xenogamy, autogamy is completely excluded. In an experiment to isolate individual flowers, 100% of isolated pistillate and bisexual flowers dried up without fertilization. In an experiment on artificial pollination of flowers, 85% (17 out of 20 flowers) of pistillate flowers formed fruits, whereas only 10% (3 out of 30 flowers) of bisexual flowers formed fruits. There were no significant differences in the number of flowers on the generative shoot in female and hermaphrodite individuals. Significant differences were found between heterosexual individuals in terms of the number of fruits and the number of seeds per generative shoot: female individuals formed 16.1-22.1 times more fruits and 13.8-28.3 times more seeds than hermaphrodites. Pistillate flowers formed an average of 1.85 ± 0.08 seeds per flower, and bisexual flowers 0.07 ± 0.02 seeds per flower, i.e., on average, female plants form 26.4 times more seeds than hermaphrodites. It was found that the fruits and seeds were formed mainly by female individuals, but hermaphrodite individuals produced the pollen necessary for fertilization. The different degree of sexual differentiation of G. asiaticum and Geranium sylvaticum L. suggests that in genus Geranium there are transformations in direction of the formation of dioecy.