Pollination needs of arrowleaf balsamroot, Balsamorhiza sagittata (Heliantheae: Asteraceae)

Arrowleaf balsamroot, Balsamorhiza sagittata (Pursh) Nutt, is a common, sometimes dominant, long-lived forb that flowers early in spring from the foothills to upper-montane areas of the northern Rocky Mountains and Intermountain West. Public land managers desire its seed for rangeland rehabilitation. Through manual pollination field trials, the species was found to have a mixed pollination system. It is primarily xenogamous (46% of ovules yielded plump achenes) but partially self-compatible (31% of achenes were plump). Unvisited flower heads formed virtually no mature achenes; only plump achenes contained seeds with endosperm. Freely visited flower heads in 2 populations produced as many achenes as manual outcross pollinations of flower heads, suggesting that seed production was not pollinator limited. Two species of Osmia bees rely mostly on Balsamorhiza and its close relative, Wyethia, for pollen. At least 165 females per hectare will need to be stocked to achieve thorough flower visitation in cultivated seed production fields