TEMPORAL VARIATION OF GENDER IN ARALIA HISPIDA VENT. (ARALIACEAE)

In many flowering plants inbreeding may be reduced by dichogamy, a difference in the timing of dehiscence of anthers and receptivity of stigmas in individual flowers. However, considerable geitonogamy (inter-flower pollination on an individual) can occur if flowers on the same plant are in different developmental conditions. Restriction of geitonogamy can be achieved if all flowers on an individual at a given time are in the same sexual phase. This condition is particularly well documented in the Umbelliferae where plants alternate between male and female functions several times, as synchronized cohorts of umbels bloom sequentially (MUller, 1883; Ponomarev, 1960; Cruden and Hermann-Parker, 1977). Temporal differences in the functioning of male and female organs of flowering plants are a common feature of moneecious and andromonoecious taxa (MaeKawa, 1924; Lloyd, 1972; Gilbert, 1975; De Jong, 1976; Bawa, 1977; Frankel and Galun, 1977; Webb, 1979; Primack and Lloyd, 1980). Nevertheless, the description and functional analysis of these complex sexual systems have lacked a firm theoretical basis (Charlesworth and Charlesworth, 1979). The recent formulation of techniques for the measurement of gender expression in plant populations (Lloyd, 1979, 1980) has aided the development of quantitative approaches to plant mating systems. Such quantification is likely to assume new importance in light of the recent proposals by Willson (1979),