Fragrant popcornflower (Plagiobothrys figuratus) COSEWIC assessment and status report: chapter 6

Biology

Life cycle and reproduction

Fragrant popcornflower is an annual herb restricted to moist open habitats at low elevations. Flower stalks develop in early summer, with flowering commencing in May or June. Flowering is indeterminate and each plant may produce several flowering stems. Reproduction is by seed, with each flower producing two to four, one-seeded nutlets. By mid-summer, when drought conditions are prevalent, seed set has occurred and the plants die. In ideal conditions, the species has the potential to form dense monospecific patches.

Amsberry (2001) reports that the seeds of Plagiobothyrs hirtus (rough popcornflower) begin to germinate with the initiation of rains in the autumn, the seedlings overwintering as submerged vegetative rosettes. It is likewise possible that the vegetative period of fragrant popcornflower commences in the fall and extends through the winter. However, this has not been documented.

The population dynamics of fragrant popcornflower have not been studied, either in Canada or the U.S. Information on demographic traits such as survivorship, recruitment rates, seed banking and seed set is also lacking. Consequently, it is not possible to draw comparisons between the intrinsic viability of fragrant popcornflower in British Columbia and that of populations further to the south.

Information on the pollination system in this species is also lacking. However, the related Plagiobothyrs hirtus is reported to reproduce largely by insect-aided cross-pollination and partially by self-pollination (USFWS 2003). In the greenhouse, 65 to 95 percent of field-collected P. hirtus seed germinated within 5 days, provided the germination medium was adequately moist. Germination of this species was also prolific in the field, with up to 78 seedlings present per 10 cm² plot after natural seed dispersal from introduced plants (Amsberry 2001). Because of this, P. hirtus is rated high in terms of recovery potential (USFWS 2003).

Herbivory

Livestock are not known to graze preferentially on fragrant popcornflower (NatureServe 2005). However, observations of the closely related Plagiobothrys figuratus ssp. corallicarpus in Oregon indicate that heavy grazing by livestock has a strong negative effect on that species (Brock 1993). Parcels of land that receive continuous grazing appear to have no P. figuratus spp. corallicarpus plants on them while adjacent properties that have little or no grazing contain vigorous populations. It appears that populations are able to rebound or re-colonize an area when grazing is removed if there is a soil seed bank or nearby seed source (Brock 1993).

Caterpillars and aphids have been observed eating foliage and flowers of the sympatrically occurring Plagiobothrys hirtus in Oregon, and plants showing evidence of herbivory by deer and small rodents have also been documented (USFWS 2003).

Dispersal

Dispersal patterns in fragrant popcornflower are unknown; however, aside from some surface texturing on the nutlets, there does not appear to be any innate seed dispersal mechanism. It is possible, given its preferred habitat, that the species relies partly on water transportation to disperse its seeds.

Interspecific interactions

In a recent study, Ingham and Wilson (1999) report that fragrant popcornflower forms a close mycorrhizal relationship with vesicular-arbuscular mycorrhizal fungi (VAMF) in its western Oregon habitat. This is the first report of mycorrhizal colonization of this species and could have important implications for the restoration of fragrant popcornflower to its native habitat in British Columbia and elsewhere. Successful reintroduction of this species may depend on the presence of sufficient VAMF innoculum at reintroduction sites (Ingham and Wilson 1999).

The interactions of fragrant popcornflower with other organisms present in its ecosystem have not yet been well-studied. Beetles use the flowers of Plagiobothrys hirtus for breeding platforms, and spiders are often seen hunting in the dense foliage in summer. Native ctenuchid moths (Ctenucha) are also seen consistently on plants of the latter species throughout the spring and summer, and have been observed obtaining nectar from the flowers, but the importance of the flower to the moth, or vice versa, is not known (USFWS 2003).

Adaptability

Seeds of fragrant popcornflower are available commercially from plant nurseries in both the U.S. and U.K. (e.g., Annie’s Annuals and Perennials 2007), suggesting this species is hardy enough to be grown under typical garden conditions and thus may be a good candidate for reintroduction into the wild.

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