Montana Field Guide

PLANTS: Well-developed shrubs of 5–80 cm height with fibrous roots and adventitious buds that can sprout after fire (FNA 2006; Lesica et al. 2012). Plants are pale gray to gray-green and densely tomentose and aromatic (Lesica et al. 2012).

LEAVES: 1–3 cm long and deeply divided into linear or linear-oblong segments divided distally into 3 linear lobes.

INFLORESCENCE: Paniculate. Bracts that subtend the flowers are linear and entire.

Our plants are subspecies tripartita. Montana’s report of Artemisia tripartita ssp. rupicola is based on a MONT specimen (accession 56976) that was mislabelled and was actually collected in Wyoming. Subspecies rupicola is only known from Wyoming (FNA 2006).

Subspecies tripartita flowers mid- summer to late fall (FNA 2006).

Subspecies tripartita is a taller shrub (when compared to subspecies rupicola) ranging from 20-80 cm in height. Leaf lobes are linear and less than or equal to 0.7 mm width (ssp. rupicola leaf lobes are 1-1.5 mm wide).

Subspecies tripartita lives in sandy to clay soils of sagebrush steppe; valleys to subalpine (Lesica 2012 et al.). Deep loam soils, usually igneous in origin and at elevations from 900 to 1900 meters (FNA 2006).

Sagebrush in general is adapted to climates with cold winters where most precipitation falls in the winter (Meyer 2008). Shrubs in the genus Artemisia are important winter browse for ungulates (Meyer 2008). This species relies on wind for pollination and seed dispersal (Meyer 2008). Each seed is enclosed in a papery pericarp. The pericarp has mucilaginous nerves that may help the seed stick to the soil while its root penetrates (Meyer 2008).

Subspecies tripartita may be one of the parents involved in the presumed hybrid origin of Artemisia arbuscula ssp. thermopola.

Artemisia tripartita ssp. tripartita flowering heads are in paniculiform or spiciform arrays of (5-)8-15(-35) cm by 0.5-1.0 cm (FNA 2006). The involucre is turbinate, 1.5-3 mm wide and 2.5–3.5 mm tall; the outer phyllaries are green and canescent while the inner phyllaries are brown to purple and glandular (Lesica et al 2012). The receptacle is glabrous. Heads are comprised of 3 to 11 disk flowers that are perfect, glandular, and have yellow to reddish corollas of 1.5–2 mm length (Lesica et al. 2012). Achenes are glabrous or resinous and about 2 mm long (Lesica et al. 2012).

In the Snake River and Columbia River basins, much of the habitat for subspecies tripartita has been lost to farming, and some populations occur as isolated islands along drainages and at the bases of mountain slopes (FNA 2006).