Golden paintbrush (Castilleja levisecta) COSEWIC assessment and status report: chapter 3

Species Information

Name and classification

Scientific name:

Castilleja levisecta Greenm.

Common names:

golden paintbrush, golden Indian paintbrush

Family:

Orobanchaceae, broomrape family

Major plant group:

Eudicot flowering plant

Golden paintbrush is a well-defined species with no commonly used synonyms or infraspecific elements (ITIS 2006).

Morphological description 

Golden paintbrush is a perennial herb from a somewhat woody base that usually produces several clustered stems (Figure 1). Flowering shoots tend to be 10-50 cm tall, unbranched, and sticky with long, soft, glandular hairs (especially near the top of the stem). The leaves are alternately arranged along the stem and usually hairy. The lower leaves are narrowly lance-shaped, grading upwards into oblong-egg-shaped leaves with 1-3 pairs of short lateral lobes. The inflorescence is a prominently bracted terminal spike. The bracts are hairy, large, golden yellow, blunt and about as wide as the upper leaves. The tips of the bracts have 1-3 pairs of short lobes. The flowers, which are largely concealed by the bracts, are bilaterally symmetric. The calyx (outer circle of flower parts) is long-hairy and deeply split into two lobes, each of which is narrowly divided into 2 linear, blunt segments. The corolla, lying inside the calyx, consists of fused petals that form a 2-lipped structure at the end of a corolla tube. The upper lip is beak-like and 3-4 times as long as the lower lip. There are four stamens and a single stigma and style. Fertilized ovaries develop into a dry capsule that contains 70-150 minute seeds which have a loose, net-veined seed coat. The large golden yellow bracts of the inflorescence distinguish golden paintbrush from other closely related species within its range in Canada (Douglas et al. 2000).

Genetic description 

Golden paintbrush has a chromosome count of 2n=24 (Heckard ex Egger pers. comm. 2006). Studies of allozyme diversity in golden paintbrush across its global range determined that exceptionally high levels of genetic diversity are maintained within the species compared with other narrowly endemic plant species. The high levels of genetic diversity are attributed to the fact that several populations are quite large, multiple generations exist within populations, that the species are perennial, and that genetic diversity may be preserved through seed-banking. The Trial Island population, though one of the most geographically isolated, was the most genetically diverse and showed relatively low levels of genetic divergence. In contrast, the Alpha Islet population showed the second highest level of genetic convergence but only modest levels of genetic diversity (Godt et al. 2005).

Designatable units 

There is only a single designatable unit since the two extant populations occur within a small geographical area in the same ecozone.

Figure 1. Illustration of golden paintbrush growth form and enlarged floral parts: floral bract (left), a single corolla (centre), and a calyx (J.R. Janish from Hitchcock et al. 1959 with permission).

Figure 1.   Illustration of golden paintbrush growth form and enlarged floral parts

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