Pollination Ecology and Endemic Adaptation of Pedicularis howellii Gray (Scrophulariaceae)

Publisher Website
Google Scholar
Abstract
Pedicularis howellii, endemic to the Siskiyou Mountains of California‐Oregon, is a root hemiparasite obligately dependent upon bumblebee pollinators that remove pollen by vibration from its short‐tubed, nectarless, rostrate flowers, which reflect visible and ultraviolet (360nm) light attractive toBombusforagers. All sixBombusspecies in the study area pollinated the plant, but only on P.howelliiandP. racemosa were B. mixtus workersthe most abundant pollinators among the seven bumblebee‐pollinated plants studied, includingDelphinium decorum, Dodecatheon jeffreyi, Penstemon newberryi, P. shastensis, and Phacelia heterophylla. Analysis of corbicular pollen loads of Bombuspollinators indicated that pollen foragers on Pedicularis species were less pollen‐constant than all other bumblebee pollinators. AlthoughP. howelliiandP. racemosablooming periods overlapped slightly, phenological isolation of blooming periods of plants sharing the same pollinators was not evident. Chemical soil analysis of its habitat and quadrat analysis of the population structure ofPedicularis howelliiindicated that the plant grows in a moderately fertile forest soil and is restricted to the edge of forest canopy openings where sunlight favors development of plants to the flowering stage. The endemism ofP. howelliiis related to a similar “edge effect” survival ofP. furbishiaein a boreal forest riparian habitat previously studied.