Montana Field Guide

Slender Indian Paintbrush is a perennial with slender, erect or ascending, usually unbranched stems, 20-50 cm tall, that often root at the base. The entire-margined leaves are narrowly lance-shaped, and the foliage is glabrous or covered with long, soft hairs. The inflorescence is generally yellow, but may be orange or even red. The oblong flower bracts are entire-margined or may have a single pair of small lobes near the top. The calyx is 15-22 mm long and deeply divided into two lobes at the top that are each divided again into two smaller, pointed lobes. The petals of the flower are united into a tube below that forms a large, galea and three small lobes or teeth opposite it. The entire corolla is 20-30 mm long; the galea is densely hairy and less than half as long as the tube, while the lip is green and ca. 1/5 the length of the galea.

Flowering occurs from June to August.

Castilleja sulphurea and C. miniata are also perennial species of paintbrush that occur in mid-elevation wetland and riparian habitats. However, both have clumped stems arising from a branched rootcrown and are not rhizomatous.

Dorn (1988, Vascular Plants of Wyoming) considers C. gracillima to be simply a rhizomatous form of C. miniata. Plants similar to C. gracillima occur in southern B.C. and Glacier National Park, Montana (=C. amplifolia) but are referred to C. miniata (Hitchcock et al., 1959, Vascular Plants of the Pacific Northwest, Vol.4).

Castilleja gracillima occurs on saturated soils along willow-dominated stream courses in sagebrush-grassland settings (Vanderhorst and Heidel 1995). In the Gallatin National Forest, it has been found in wet meadows with at least seasonally saturated soils, along streambanks and on gentle sloping spring terraces (Matthews (1989). Associates include Castilleja minata (scarlet paintbrush), Geranium richardsonii (white geranium), Salix wolfii (Wolf's willow), Epilobium glaberrimum (smooth willow-herb), Habenaria dilatata (white bog-orchid), and Habenaria hyperborea (northern green bog-orchid).

Species of the genus Castilleja are typically hemiparasites, capable of growing with or without deriving supplemental nutrition from a host plant. They are generally pollinated by hummingbirds and insects, and produce many seeds that are very light and easily airborne (Matthews 1989). Species of Castilleja are subject to herbivory by noctuid larvae, however, slender Indian paintbrush was not observed to be as heavily fed upon as many other species.

Matthews reported populations in the Gallatin National Forest as apparently stable. However, they may be subject to natural disturbance regimes, since cycles of disturbance and re-establishment occur at relatively frequent intervals in the stream and river bank habitats where this species grows.

POLLINATORS
The following animal species have been reported as pollinators of this plant species or its genus where their geographic ranges overlap: Bombus appositus, Bombus bifarius, Bombus fervidus, Bombus flavifrons, Bombus melanopygus, Bombus sylvicola, Bombus occidentalis, and Bombus kirbiellus (Macior 1974, Thorp et al. 1983, Bauer 1983, Mayer et al. 2000, Wilson et al. 2010, Pyke et al. 2012, Koch et al. 2012, Miller-Struttmann and Galen 2014, Williams et al. 2014).

Recreational fishing is the primary activity where this plant grows in the Gallatin National Forest, and is not thought to affect it (Mathews 1989). Livestock grazing takes place in these drainages, however population monitoring would be needed to detect any impacts.

STATE THREAT SCORE REASON
Reported threats to Montana's populations of Slender Indian Paintbrush include the potential threat of trampling from anglers at populations located along the Gallatin River in Yellowstone National Park. (MTNHP Threat Assessment 2021).