Pollination Ecology of Pedicularis palustris L. (Scrophulariaceae) in North America

Abstract Field collections and measurements of corolla tubes and Bombus tongues indicated that Pedicularis palustris , an early summer‐blooming plant on Ile aux Grues and Ile aux Oies in the St. Lawrence River, Canada, is pollinated nototribically by queens of four species of bumblebees foraging for nectar and sternotribically by three species of Bombus workers scraping pollen from anthers concealed in the galea. Short‐tongued workers of B. terricola secured nectar by perforating the base of the corolla tube dorsally or ventrally and, in some cases, pollinated the flower while robbing nectar. The flowers are insect‐dependent for pollination and are almost exclusively bumblebee‐pollinated. Sugar concentration of nectar, determined by refractometry, ranged from 8.0% to 19.5% (mean = 13.9%), and fructose and sucrose components of nectar samples from North America and the Netherlands were detected by thin‐layer chromatography. Excavated roots of Pedicularis palustris confirmed its root‐hemiparasitism. Parallel pollination studies were carried out on Hypericum perforatum and Vicia cracca on the mainland in the same area which bloomed later than Pedicularis and were pollinated primarily by Bombus workers. Predominance of queen pollinators on Pedicularis and worker foragers on Hypericum and Vicia and analysis of corbicular pollen loads of foragers suggest a phenological relationship between Pedicularis palustris and the annual reproductive cycle of its bumblebee pollinators previously derived from investigations of other North American and Japanese species.