The floral ecology and breeding system of Veratrum virginicum (Melanthiaceae)1

We analyzed the floral biology of a population of the threatened/endangered Veratrum virginicum (L.) W.T. Aiton at the Shaw Nature Reserve (Missouri, USA), comparing our results to the first and only study of this species by Charles Robertson (1896). We confirmed most of Robertson's original descriptions regarding floral presentation, protandry, and insect pollination but found the following new information. Each flower lived 9–11 days and smelled of raw liver and latex. We discerned four floral stages based on gradual changes in style and stamen orientation, which might assist in insect-mediated pollination. We determined that stigmas became receptive by the fifth day of anthesis. The generalist pollination system included three Lasioglossum species (Halictidae) and the beetle Chauliognathus marginatus Fabr. (Cantharidae). Most floral foragers showed a geometric mean of body dimensions between 2–3 mm. Approximately 40% of foraging insects carried heterospecific pollen loads, combining the host flower's pollen with grains from up to seven co-blooming taxa. Field observations suggest that all bees foraged on multiple inflorescences whereas beetles remained on the same inflorescence for hours. Larger Apidae species showed symptoms of nectar poisoning. Epifluorescence showed that flowers exposed to visiting insects contained < 5 pollen tubes per gynoecium. Fruit set was 3% for bagged flowers and 51% for exposed flowers. However, the conversion rate of ovules into seeds was low in both bagged (2%) and exposed (6%) flowers. We interpret low reproductive success as one explanation for current declines in populations of this species.