Bumblebee pollination of Cypripedium macranthos var. rebunense (Orchidaceae); a possible case of floral mimicry of Pedicularis schistostegia (Orobanchaceae)

Abstract

Nectarless flowers of Cypripedium macranthos var. rebunense are pollinated by only queen Bombus pseudobaicalensis, which also pollinates nectar-producing flowers of Pedicularis schistostegia. Our previous study (Sugiura et al. 2001) suggested that they form a floral mimicry system: (1) Flowering phenology of both plants overlapped greatly. (2) Cypripedium occurred with lower frequency relative to Pedicularis. And (3) in a mixed stand of both plants, foraging bumblebees were sometimes confused between the mimic and model flowers. The present study clarified the system with new evidence. (4) Flower colour of Cypripedium and Pedicularis would be similar within the range of a bumblebee's visual spectrum. And (5) both species largely overlapped in spatial distribution. Based on these findings, we discuss how C. macranthos var. rebunense differs in pollination mechanism from other congeneric species, especially C. calceolus.