WIND POLLINATION IN HIGH-MOUNTAIN POPULATIONS OF HORMATHOPHYLLA-SPINOSA (CRUCIFERAE)

In this paper we study aspects of the breeding system of Hormathophyll a spinosa (Cruciferae) to identify the factors responsible for seed pr oduction in the absence of insect pollinators. The pollinator-exclusio n experiments show that H. spinosa, under natural conditions, does not produce seed by apomixis or spontaneous autogamy. H. spinosa appears to be self-incompatible but slightly geitonogamous. Thus, this plant s pecies needs pollen vectors for reproduction. The results of the wind- exclusion experiments performed during two different years in two popu lations of H. spinosa support the hypothesis that the wind acts as a p ollen vector; flowers excluded from the wind had a lower fruit set and female fertility than Bowers excluded from all pollinator insects (wi nged and wingless). This generalist pollination system (insects and wi nd) permits this species to colonize and sustain viable populations in high mountains, where this species is the only woody shrub living abo ve 3000 m above sea level in the Sierra Nevada.