Pollination biology of Rhododendron cyanocarpum (Ericaceae): An alpine species endemic to NW Yunnan, China

The pollination biology of Rhododendron cyanocarpum (Franch.) W. W. Smith, an alpine species endemic to NW Yunnan, China, was investigated between 2007 and 2008. Floral traits including flowering time, floral morphology, petal color, and floral scents were assessed, and the associated pollinator assemblage and their foraging behavior were recorded. The flowering period of R. cyanocarpum ranges from late March to middle May and a single flower can last 8-10 days in its natural habitat. Flowers generally show marked herkogamy and the protruding style encourages pollinator foraging behavior that counteracts self-pollination. Floral scents comprise mostly aliphatics (64.37%) and terpenoids (29.88%), which make the flowers attractive for several insect groups, but a peak at 430nm in the reflectance spectrum of petals suggest selection for the attraction of bumblebees. The two Bombus species, B. festivus and B. richardsiellus, representing 90% of total recorded visits, were the only insect species that can be considered to effectively pollinate R. cyanocarpum. Pollination treatments indicated the general self-compatibility of R. cyanocarpum; however, outcrossing seemed to be the dominant strategy, with low rates of self-fertilization providing a certain level of reproductive assurance in its alpine habitat.