Pollination ecology and breeding systems of Cypripedium kentuckiense (Orchidaceae) in Tennessee1

Abstract

The orchid Cypripedium kentuckiense is listed as imperiled in Tennessee and Oklahoma and critically imperiled in seven other states. We followed individuals' vegetative and floral traits over two seasons. Patterns of floral senescence were found to vary over two seasons and might be related to April temperatures when buds develop. Mechanical self-pollination was uncommon but perhaps “leaky.” Frequencies of insect-mediated pollination were surprisingly high (62%) for a Cypripedium species with large flowers but conversion of flowers into fruit was low (7% and 14%), suggesting that cryptic factors lower reproductive success, not inadequate pollinator visits. Hand-pollinations suggest flowers are self-compatible. As in other Cypripedium species, floral architecture relates to pollinator dimensions but at this site, only two bee species, Anthophora abrupta and A. bomboides, were primary pollinators. Male A. abrupta were common visitors although male bees are uncommon pollen vectors of Cypripedium species. For the first time, exit patterns of bees inside Cypripedium flowers were recorded based on bee species and gender. This behavior varied and was somewhat atypical of previous studies on other bee-pollinated species in the clade and genus. Specifically, Anthophora species within labella chewed on the epidermis lingering within the interior and exit canals. Consequently, C. kentuckiense might not be a trap.