The Annual Cycle of Osyris Quadripartita, A Hemiparasitic Dioecious Shrub of Mediterranean Scrublands

Abstract

(1) The growth, flowering and fruiting phenology of a southern Spanish population of Osyris quadripartita (Santalaceae), an evergreen dioecious shrub of Mediterranean habitats, has been studied over a 5-year period. (2) The growth season encompasses the period November-August for females and virtually the entire year for males. Males resume growth shortly after the autumn rains, at least 1.5 months in advance of females. The mean length of the growing period was significantly longer for males. (3) The flowering period lasts for nearly 6 months (March-September) for females and nearly the entire year for males, with a peak in May-June. The flowering peak of males encompassed that of females in all years. The mean length of the flowering period was significantly longer for males. (4) Ripe fruits are produced throughout the year, with a major peak in winter and a minor one in spring. (5) The phenological pattern of 0. quadripartita seems to be shared only by species from tropical forests or by others that, like itself, are survivors of an old evergreen tropical flora currently living in Mediterranean refugia. Its phenology seems, therefore, not to have experienced substantial variation since the initiation of the Mediterranean climate in the Pliocene. The hemiparasitic habit must have contributed to the persistence, in a strongly seasonal climate, of virtually continuous physiological activity throughout the year. (6) Sexual differences in phenology are interpreted in terms of the constraints imposed on the organization of the female annual cycle by fruit development and maturation. Males are relieved of this function and allocate the available time among fewer activities. As a result, they exhibit longer average durations of individual functions, greater seasonal spacing of functions, and more flexible integration of activities, than do female plants.