Reproductive biology of viscum cruciatum (viscaceae) in southern spain

Abstract

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 pollen grains, and has a dry mass of 14 mg, and thus a low relative staminate effort (RSE) value of 4,059. Female flowers, 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 significantly less fruit than control branches open to natural pollination. 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 embryo production does not take place in this species and cannot be the cause 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 fusion of the chlorophyllous endosperm. Fruit size is not correlated with the number of embryos per "seed" but probably with other ecological or maternal factors. Although a dormancy period was not observed, flowering and fruiting are restricted mainly to winter. Nevertheless, the pattern of flowering differed significantly between the two years studied, being longer and less overlapping during 1991 (only in the females). The fruit set was also lower in 1991.