REPRODUCTIVE-BIOLOGY OF CISTUS-LADANIFER (CISTACEAE)

The phenology, major floral characteristics, fruiting levels, and bree ding system of Cistus ladanifer L. (Cistaceae), a common western Medit erranean shrub species, were studied in a southern Spanish population. The white, large (64 mm in diameter) flowers of this shrub appear dur ing spring (March-May) and produce abundant pollen and nectar. In the year of study, flowers lasted up to three days, during which they were visited by a diverse array of insects including beetles, flies, and b ees. Hand-pollinations revealed that flowers do not set any seed unles s cross pollen is applied to the stigma. Microscopical observations in dicate that self pollen tubes grow down the stigma but invariably fail to induce fruit maturation. At the plant level, all estimates of fecu ndity investigated (number of seeds per capsule, proportion of ovules developing into seed, and proportion of flowers setting fruit) were hi ghly dependent on nearest neighbour distance, with isolated plants set ting as little as 0% fruit. In contrast, plants within a clump often t ransformed into fruit as much as 90% of the flowers. At the population level, seed output was estimated to range between 3,000 and 270,000 s eeds per plant during 1991.