Cusick's Horsemint - Agastache cusickii
State Rank Reason (see State Rank above)
This species is known in Montana from only a few locations in the Tendoy and Beaverhead Mountains. The steeply sloping habitat and relative remoteness of most populations minimizes its vulnerability to grazing and timber harvest -- the principle current land uses. However, these slopes can be vulnerable to destabilization if impacted by activities such as mining or road maintenance; the largest occurrence is in an area that is quarried for rock/gravel.
Cusick's Horse-mint is an herbaceous, long-lived perennial with numerous stems, woody at the base arising from a branched rootcrown surmounting a taproot. Plants are 1-2 dm high, but the stems often lie prostrate beneath the surface spreading from the rootcrown. Opposite leaves have blades that are 1-2 cm long and triangular with a rounded base and a petiole that is up to 1 cm long. Foliage is covered with fine, short hairs. White flowers are borne amongst purple-tipped bracts in a head-like inflorescence that is 1.5-4 cm long. The tubular corolla is 8-12 mm long, and the purple-tinged calyx is tubular with 5 pointed lobes. The 5 stamens are exserted from the mouth of the flower tube.
Flowering occurs in late June and July.
The related nettle-leaf horsemint (Agastache urticifolia) is taller (at least 4 dm) and has larger leaves.
Harney & Malheur Cos., Oregon and at scattered locations in the mountains of central Idaho, northern and central Nevada, southwesternmost Montana, and possibly northeastern California; in Steens, Santa Rosa, White Pine, and Toiyabe Mountains of Nevada.
Observations in Montana Natural Heritage Program Database
Number of Observations:
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(Observations spanning multiple months or years are excluded from time charts)
In the Tendoy Mountains, Cusick's horesmint grows on open slopes with little vegetation cover. The populations are primarily on steep, loose talus below limestone outcrops, often in chutes, with a few plants usually occupying talus deposits at the base of the slope. On the Beaverhead National Forest, this species is confined to the south-facing slopes of narrow canyons, across a wide range of elevations (Vanderhorst 1995). One lower-elevation occurrence occupies the slope above a broad valley.
Woody dominants include limber pine, Douglas fir, mountain mahogany (Cercocarpus ledifolius), big sagebrush (Artemisia tridentata), and a gooseberry (Ribes setosum). Major grasses include bluebunch wheatgrass and spike-fescue (Leucopoa kingii). Frequently associated forbs include the talus-adapted perennials Arenaria nuttallii, Oenothera caespitosa, Phacelia hastata, and Penstemon montanus, and annuals such as Collinsia parviflora and Polygonum douglasii.
Ecological Systems Associated with this Species
Agastache cusickii seems to be confined to areas of smaller-size talus. The substrate is constantly settling and shifting and is easily disturbed. Soil development is minimal on the limestone talus where the species grows in the Tendoys, however at one site where the banks have been cut by quarrying, some horizonation was noted (Vanderhorst 1995). The upper zone of the talus is extremely well-drained, however clays provide a higher water-holding capacity in the lower zone. This steep habitat is not generally susceptible to fire; the species may sprout from the caudex following disturbance (USDA, Fire Effects Information System, http://www.fs.fed.us/database/feis/).
This species' habitat is by nature easily disturbed, however all occurrences on the Beaverhead National Forest are in remote, relatively undisturbed sites (Vanderhorst 1995). The steepness of this habitat tends to make it inaccessible to cattle, and the timber on these slopes is not of commercial quality (Vanderhorst 1995).
One large population on a lower-elevation valley slope lies along a major gravel road, where past quarrying of limestone talus has reduced the habitat extent, and road maintenance could impact bank stability. Roads are also found in some canyon bottoms where the species occurs, but these are infrequently traveled. Future road improvement or maintenance and other canyon-bottom activities could be managed to avoid impacting the populations and habitat.
- Additional ReferencesLegend: View Online Publication
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- Lesica, P., M. T. Lavin, and P. F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
- U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. 2000. Fire Effects Information System
- Vanderhorst, J.P. and P. Lesica. 1994. Sensitive plant survey in the Tendoy Mountains, Beaverhead County, Montana. Unpublished report to the Bureau of Land Management, Butte District. Montana Natural Heritage Program, Helena, MT. 59 pp. plus appendices.