Reproductive Biology of the Orchid Cleistes divaricata (L.) Ames var. bifaria Fernald Growing in a West Virginia Meadow

ABSTRACT
A population of Cleistes <em>divaricata</em> (L.) Ames var. <em>bifaria</em> Fernald, at its northwesternmost range limit and rare in West Virginia, more than quadrupled in numbers between 1980 and 1986 in an acidic, nutrient-deficient West Virginia meadow that is mowed annually. The aerial, upright ramicauls (stems) may be vegetative with one to three leaves; when flowering, they typically bear one flower, one cauline leaf, and a floral bract. Long-lived flowers exploit naive bees, operating as rewardless bee-food-flower mimics. A hinged anther drops clumps of pollen tetrads onto the dorsal thorax of <em>Bombus</em> and <em>Megachile</em> workers. Pollination is effected when bees deposit pollen in flowers visited subsequently. Field capsules with 120 to 11,000+ seeds result from xenogamous and geitonogamous pollinations. Scarcity of pollinators and occasional severe herbivory of flowers and capsules lower reproductive output. Reproduction is enhanced by production of healthy pollen, low pollen to seed ratio, a highly efficient pollination mechanism, and high embryo viability.