Tall bugbane (Cimicifuga elata) COSEWIC assessment and status report: chapter 6

Biology

There is no information available on the biology of Cimicifuga elata in British Columbia. However, research has been conducted on populations in Washington and Oregon, where it is relatively more abundant. Their studies have focused on pollination ecology, including evolutionary implications (Pellmyr, 1985; Pellmyr, 1985a ; Pellmyr, 1986), and population genetic structure, including implications associated with its rarity (Evans, 1993). There have also been studies on the presence of active compounds of pharmacological use in species of Cimicifuga, particularly in the Far East (Shibata et al., 1980).

Phenology

Young plants of Cimicifuga elata emerge in the spring, produce buds in late spring, and flower mid-late June, July, or even into August. In experiments done by Kaye and Kirkland (1994) seeds appear to require cold-stratification for germination and percentage germination was low. Seeds are heavy and no special dispersal mechanism is known (Kaye and Kirkland, 1994). In growth experiments on C. elata using ample light (Anonymous, 1996), plants grew to reproductive size in three years. Under less ideal conditions, time to reproductive size could be six years. Plants growing in mature forest were rarely observed flowering, whereas plants in openings had large inflorescences.

Pollination Biology

This species is pollinated by bumblebees, solitary bees, the introduced honeybee, and syrphid flies. Flowers of C. elata have also been visited by beetles, and small, pollen-foraging flies (Pellmyr, 1986). Evans (1992) observed solitary bees more than any other pollinator on the flowers of C. elata. Cimicifuga elata is poorly adapted to out-crossing, is a poor competitor for pollinators, and is self-compatible. Flowers of C. elata have no nectar offering little reward, and resulting in few visits from pollinators. Furthermore, corollas are not showy, there are no markings to guide pollinators, and no special structures to apply pollen to bodies of pollinators, all features that tend to lead to self-pollination (Evans, 1992). A reduced number of staminodia also lends itself to selfing (Pellmyr, 1985a). Usually staminodia are completely absent from this species (Evans, 1992). In addition, C. elata occurs in habitats that contain few attractive-flowering species, and therefore, it cannot benefit from their increased ability to attract pollinators. Pollination is geitonogamous, or flower to flower on the same plant (self-pollination), ensuring success in a single visit (Pellmyr, 1986). Flowering occurs sequentially within the raceme, with individual flowers blooming at different times, extending the flowering period, which, unlike previously mentioned characteristics, maximizes the chance of cross-pollination. Evans (1992) found that the blooming period varied from 19 to 47 days, and that 10 out of every 23 flowers was the average flowering ratio. A larger floral display does not appear to incur greater success in cross-pollination for C. elata; it is more likely that density of flowers in a population has a greater effect on reproductive success (Pellmyr, 1986).

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