Sexual differences in year‐to‐year flowering trends in the dioecious multi‐stemmed shrub Lindera triloba : effects of light and clonal integration

Summary 1.  To obtain information on mechanisms underlying between‐sex differences in flowering patterns of dioecious plants, we tested two hypotheses: first, that sexual differences in year‐to‐year flowering variations result from differences in sensitivity to inter‐annual variations of environmental factors and second, that the degree to which physiological integration within genets controls the flowering of ramets differs between the sexes. 2.  The flowering patterns of a dioecious multi‐stemmed understorey shrub, Lindera triloba , were monitored both at the ramet and genet levels over five consecutive years in a 4‐ha plot. 3.  The numbers of flowering genets of both sexes fluctuated annually and were positively related to the hours of sunshine during July and August in the previous year. The number of flowering ramets within genets and inflorescence numbers within ramets or genets tended to be larger for male genets than for female genets. There was significant inter‐annual variation in the number of flowering ramets within male genets, but not within female genets. Although both sexes showed significant inter‐annual variation in inflorescence numbers, the extent of variation was larger for males than females. These between‐sex differences resulted from significant relationships for male genets between their number of flowering ramets and both their total number of ramets and the number of hours of sunshine they experienced, whereas there were no such relationships for female genets. 4.  There were also between‐sex differences in the probability of flowering and inflorescence production of individual ramets within genets: male ramets exhibited a stronger sensitivity of flowering than females to the growth status of the genets to which they belonged. This suggests that individual ramets within genets bloom in an integrated manner rather than in an autonomous manner, and that the magnitude of integrated flowering of ramets differs between sexes. 5.   Synthesis . This study not only measured flowering at the whole‐plant level but also showed that flowering patterns of the lower‐level module were controlled within the higher‐level module differently by male and female plants. Future studies should be designed to consider environmental variation between years and modular integrations, when investigating differences between the sexes during the reproduction of dioecious plants.