Pollen-like trichomes may reward pollinators of Cypripedium wardii (Orchidaceae)

We investigated the function of the white trichome tufts on and within labellum and the pollination mechanism of Cypripedium wardii. We conducted field observations on a large population over four years analyzing its floral epidermis, breeding system, and trichome consumption by its visitors. Flowers bear two tufts of white, clustered, moniliform, trichomes located on the infolded entrance to the labellum, and a third tuft is located on the floor of the labellum. These trichomes are lipid-rich and are collected by bees and consumed by hoverflies. Although self-compatible, these flowers require pollen vectors for fruit set. Trichomes of C. wardii provide a pollen surrogate potentially rewarding polylectic/polyphagic pollinators. This results into an unusually high fruit set (76%-82%) contrasting with a lower-level of fruit set in other deceptive orchids. Our findings provide new insights on the gradation between reward and deception in the evolution of orchid flowers.