REPRODUCTIVE-BIOLOGY OF VISCUM-CRUCIATUM (VISCACEAE) IN SOUTHERN SPAIN

The reproductive biology of the dioecious Viscum cruciatum, one of the few viscaceous mistletoes occurring in Europe, was investigated. The male flower is 7.2 mm long and lemon-scented, produces ca. 58,000 poll en grains, and has a dry mass of 14 mg, and thus a low relative stamin ate effort (RSE) value of 4,059. Female Bowers, ca. 3 mm long, 2.7 mg dry mass, secrete small amounts of nectar (0.05 mg sugar/d). A stigma is not apparent. Flowers inside nylon bags (i.e., insect-free) set sig nificantly less fruit than control branches open to natural pollinatio n. Pollination is performed by insects. Flowers bagged against insects but not wind set some fruit Flowers bagged with dense cloth excluding wind and insect pollination did not set any fruit. Agamospermous embr yo production does not take place in this species and cannot be the ca use of the shift in sex-ratio toward females. Fruits can contain one ( 45%), two (43.6%), three (11%), or four (0.3%) embryos, which may not be true polyembryony but may result from the partial or complete fusio n of the chlorophyllous endosperm, Fruit size is not correlated with t he number of embryos per ''seed'' but probably with other ecological o r maternal factors. Although a dormancy period was not observed, flowe ring and fruiting are restricted mainly to winter. Nevertheless, the p attern of flowering differed significantly between the two years studi ed, being longer and less overlapping during 1991 (only in the females ). The fruit set was also lower in 1991.