Grand coulee owl-clover (Orthocarpus barbatus) COSEWIC assessment and status report: chapter 8

Biology

Reproduction

Orthocarpus barbatus is a true annual and over-winters as seeds in British Columbia. Germination probably takes place in May and because of the low available moisture in the Artemisia tridentata communities, plants begin to senesce by the end of July. All flowers are chasmogamous (with flowers that open to allow pollination) and there are no asexual means of reproduction.

It appears that Orthocarpus species are predominantly outbreeders. The two contrasting breeding systems may partition the host-environment of these parasitic plants with the showy outbreeders forming compact masses in order to improve the efficiency of cross-pollination while the inbreeders are more dispersed (Atsatt 1970). It is uncertain whether O. barbatus is an inbreeder or an outbreeder-- the latter seems likely as it does have very showy flowers and the plants occur in relatively dense patches. Outbreeding Orthocarpus are primarily pollinated by honeybees and native bee species (Atsatt 1970).

Movements/dispersal

Seed dispersal is not well understood but it is likely that most seeds are not dispersed beyond the immediate vicinity of the parent (Chuang and Heckard 1983). The latter did speculate that reticulations on the coats of the small, light-weight seeds may improve aerodynamic properties important to wind-dispersal, or add surface roughness aiding in animal dispersal. Alternately, the loosely netted reticulations on the seed coat may trap air and thus add buoyancy to seeds during dispersal by water (Kuijt 1969).

The nearest USA population is about 80 km south, along highway 20 west of Okanogan in the Okanogan National Forest, Okanogan County, Washington (Mark Egger, pers. comm., 2005). Based on the localized type of dispersal mechanism for this species, rescue from US populations is unlikely.

Germination and survival

No specific information is available on germination requirements for Orthocarpus barbatus.

Nutrition and interspecific interactions

Members of the genus Orthocarpus are hemiparasites, containing chlorophyll and fix carbon through photosynthesis but receive water and nutrients through parasitic root connections (Kuijt 1969). Orthocarpus species may also obtain photosynthates and secondary compounds from their hosts (Atsatt 1970). These secondary compounds can reduce herbivory without affecting pollinators. It appears that alkaloids may be taken up in the leaves and outer floral tissues of some species but not by their nectar, which has the ultimate effect of increasing seed production and improving fitness (Adler 2000, Adler and Wink 2001, Boros et al. 1991).

Closely related species of Orthocarpus have been shown to be facultative hemiparasites capable of growing and producing flowers in the absence of a host, although shoot mass tends to be much higher in the presence of a host (Matthies 1997).

Grassland species of Orthocarpus form haustorial connections (root grafts) with a number of grassland associates including annuals and perennials of the grass, aster and a number of other families. It is likely that research results with the closely related genus Castilleja (Heckard 1962), which also forms haustorial connections with host plants, are applicable to Orthocarpus. Heckard (1962) investigated the growth of eleven species of Castilleja with, and without, hosts. All species were capable of completing their life cycle in the absence of a host. However, when they were grown in culture with non-Castilleja species, all but one species exhibited faster growth rates, produced a larger number of branches, and flowered earlier than when they were grown in isolation.

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