Current conservation status and reproductive biology of the giant tree Rhododendron in China

Abstract

The conservation status and pollination biology of Rhododendron protistum var. giganteum Balf.f. & Forrest, a plant taxon with an extremely small population size, was investigated in western Yunnan from 2014 to 2016. In addition to two previously reported populations, 7 more populations were found in the Gaoligong Mountain National Nature Reserve. Floral traits, including flowering time, floral morphology, petal color reflectance and flower scents, were assessed, and the associated probable pollinator assemblies were recorded. The flowering period of R. protistum var. giganteum was from late January to early March and a single flower can last 14–16 days in its natural habitat. Bombus and two genera of birds, Aethopyga and Dicaeum, were observed to be floral visitors, representing 75% and 25% of total recorded flower visits respectively. Floral scents matched the vegetative parts scent, indicating that scent is unlikely to be of importance in attracting pollinators, but the red flower color suggests ornithophilous pollination. A marked peak in the reflectance spectrum at 436 nm was observed, providing further evidence for bumblebee pollination. Pollination treatments indicated that pollen limitation was not severe in R. protistum var. giganteum. Overall, our preliminary report provides basic information and facilitates further conservation of R. protistum var. giganteum.