Montana Field Guide

Linearleaf Fleabane has unbranched stems that are 5-30 cm tall and which arise from a stout taproot and branched rootcrown. The mostly basal leaves are linear and 1-9 cm long. The bases of the stems and leaves are enlarged and straw-colored or purplish, and the herbage is covered with fine gray hairs. The flower heads are usually solitary at the ends of the stems. The involucral bracts are 4-7 mm long and are covered with long, appressed hairs and occasionally also with glands. The 15-45 yellow rays are 4-11 mm long and the yellow disk flowers are 3-5 mm long. There are 10-20 pappus bristles at the top of each achene.

Flowering occurs from May to early June.

Linear-leaf fleabane is our only Erigeron with yellow ray flowers. Erigeron filifolius and E. ochroleucus also have narrowly linear leaves but the ray flowers are white or blue and and E. filifolius has more than one head per stem. Members of the genus Stenotus (formerly a part of Haplopappus) have yellow rays, but the involucral bracts are in 2-3 series of different height.

Erigeron linearis occurs in dry, often rocky soil from the foothills up to moderate elevations, frequently with sagebrush (Heidel and Cooper 1998). Dominant species in its habitat include bluebunch wheatgrass and mountain big sagebrush (Artemisia tridentata ssp. vaseyana). Associated species and habitats vary widely. In the Scratchgravel Hills near Helena, it occupies two distinct habitats - one a midslope opening on a steep east-facing timbered hillside, and the other a gently southwest-facing lower slope in open rolling plains. In Beaverhead County, linear-leaf fleabane was found on granular, diabase-derived soil in rolling sagebrush steppe, where it occupied a disturbed opening dominated by Agropyron smithii, along with other species characteristic of disturbed areas, including Arenaria kingii, Bromus tectorum, Chrysopsis villosa, Haplopappus acaulis, Oxytropis sericea and Phlox bryoides. Other small populations in Beaverhead and Silver Bow counties were found in sparse vegetation.

Linear-leaf fleabane is an herbaceous perennial. At one locality in Beaverhead County, Heidel and Vanderhorst (1996) speculated that the site may have been grubbed or burned, resulting in removal of the sagebrush cover. The low stature of this plant probably means that it responds positively to the disturbance of livestock grazing.

POLLINATORS
The following animal species have been reported as pollinators of this plant species or its genus where their geographic ranges overlap: Bombus bifarius, Bombus centralis, Bombus fervidus, Bombus flavifrons, Bombus huntii, Bombus melanopygus, Bombus mixtus, Bombus rufocinctus, Bombus occidentalis, and Bombus insularis (Thorp et al. 1983, Wilson et al. 2010, Colla and Dumesh 2010, Koch et al. 2012).

Leafy spurge and spotted knapweed threaten populations in the Scratchgravel Hills. Observations suggest that this species may respond positively to disturbance. Some populations might have been established through human activity, because the species is highly localized within what appears as extensive suitable habitat, in locations of historically intense mining activity.

STATE THREAT SCORE REASON
Reported threats to Montana's populations of Linear-leaf Fleabane are primarily those associated with noxious weeds (MTNHP Threat Assessment 2021). Direct competition with Spotted Knapweed (Centaurea stoebe), Dalmatian Toadflax (Linaria dalmatica), Leafy Spurge (Euphorbia virgata) is impacting many populations, and some infestations are severe. Resulting habitat loss is exacerbated by chemical herbicide application, and surviving individuals are exposed to spray. Information on the scope, severity, and/or timing of these and other threats is needed.