Pollination Ecology of Gentiana andrewsii

Abstract

The pollination syndrome of Gentiana andrewsii Griseb., a closed, blue gentian, was investigated in a disclimax community in relation to the ecological and phenological characteristics of the surrounding plant community. Gentiana andrewsii is obligately dependent upon bumblebees for pollination and seed set. The flowers are self-fertile, protandrous, and herkogamous; pollen deposition is restricted to the bumblebee's sternum. Pollen is the primary bumblebee attractant; the sugar concentration of nectar is low. The corolla reflects a purplish-blue color augmented by a dissected pattern of ultraviolet light, both well-adapted to bumblebee vision. Bumblebee species show no preference among synchronously flowering species, but caste preferences are evident, with G. andrewsii largely attracting workers. Most local bumblebees have tongues too short to retrieve nectar from the long Gentiana corolla tubes; many steal nectar from lateral perforations of the corolla tube. The blooming of G. andrewsii at the end of the bumblebee season may have resulted from selection favoring other earlier flowering competitors. Sympatric and synchronously blooming Gentiana crinita Froel. (Gentianella crinita (Froel.) G. Don, Gentianopsis crinita (Froel.) Ma) also reflects the same purplish-blue color as G. andrewsii but with different ultraviolet reflection patterns. Nectar appears to be the primary attractant in G. crinita. Queens and larger workers are the most frequent visitors, tongue length being less of a discriminating factor.