Montana Field Guide

Lemhi beardtongue is a large perennial, with 1 to several stems reaching 70 cm in height and arising from a branched rootstock and short taproot. The leaves are narrowly lance-shaped and untoothed. Stalks of the basal leaves are up to 16 cm long, while the opposite stem leaves lack stalks and become smaller up the stem. Herbage is lightly covered with small hairs and occasionally a thin, bluish wax. Clusters of several short-stalked flowers are borne in the axils of upper leaves. The bright blue, tubular corolla is flared and two-lipped at the mouth and 25-35 mm long. The lance-shaped calyx segments taper to a long tip, are 7-11 mm long, and have a narrow white margin. Anthers are hairy with short pubescence, and the staminode is glabrous.

Flowering takes place from early June to late July, depending on climatic conditions and elevation. Fruits mature and dehisce during August and early September.

Lemhi penstemon is a tall, conspicuous plant, and easy to spot when in full bloom. Distinguishing features include the large, bright blue corollas, the sharp, narrow, elongated tips on the calyx lobes, and the lack of hairs on the staminode. Penstemon cyaneus is very similar but has sepals that are rounded at the tip and nearly as broad as long. Penstemon cyananthus also has smaller flowers that are only 15-25 mm long.

In Montana, Lemhi beardtongue occurs on moderate to steep, east- to southwest-facing slopes, often on open soils. In Beaverhead County, it generally grows below or near the lower extent of Douglas-fir and/or lodgepole pine forest, in habitat dominated by big sagebrush and bunchgrasses, including western wheatgrass and Idaho fescue. Within these habitats, Lemhi beardtongue prefers areas that are more sparsely vegetated (Shelly 1990). In the northeastern Pioneer Mountains, it inhabits forb-dominated openings in lodgepole pine and to a lesser extent Douglas-fir forest; big sage is typically not present, and prominent forbs include Astragalus miser, Pedicularis contorta and Townsendia parryi.

The species is not restricted to any particular geological substrate, and has been found on granitic soils as well as limestone and other sedimentary substrates. Soils are often very gravelly, however soil texture is highly variable and ranges from sand to fine clay. Field surveys from 1986-1989 indicate that it is most commonly found on gravelly loams. Some populations grow partially or entirely on roadbanks.

Lemhi beardtongue has some degree of adaptation to natural disturbance, as evidenced by its preference for more open habitats such as rock outcrops and steep, rocky slopes with natural soil slippage (Shelly 1990). This adaptation is underscored where plants have colonized roadbanks.

Studies have shown that seed germination and recruitment are the most critical life history stages (Heidel and Shelly 2001). In general, both flowering and germination are higher in years when spring and early summer are cool and wet. Mortality of established plants is highest in hot, dry years (Heidel and Shelly 2001). Waxing and waning of populations is expected for native species of successional habitats, like P. lemhiensis.

POLLINATORS
The Large Pollen Wasp (Pseudomasaris vespoides) is a specialist pollinator of Lemhi Beardtongue (Stucki et al. 2013). Although flowers of Lemhi Beardtongue can get visited by several insect species, the Large Pollen Wasp is a particularly efficient pollinator. Behaving more like a bee, the Large Pollen Wasp’s body fits perfectly into the flowers of Lemhi Penstemon; as the Large Pollen Wasp feeds on nectar, its body collects pollen. As a result, Lemhi Beardtongue benefits from increased seed production and improved genetic diversity while the Large Pollen Wasp gains necessary pollen to feed its larvae (Starkey 2015).

The following animal species have also been reported as pollinators of this plant species or its genus where their geographic ranges overlap: Bombus vagans, Bombus appositus, Bombus auricomus, Bombus bifarius, Bombus centralis, Bombus fervidus, Bombus flavifrons, Bombus frigidus, Bombus huntii, Bombus melanopygus, Bombus mixtus, Bombus nevadensis, Bombus rufocinctus, Bombus sylvicola, Bombus occidentalis, Bombus pensylvanicus, Bombus bimaculatus, Bombus griseocollis, Bombus impatiens, Bombus insularis, Bombus suckleyi, Bombus bohemicus, and Bombus kirbiellus (Macior 1974, Thorp et al. 1983, Bauer 1983, Mayer et al. 2000, Wilson et al. 2010, Colla and Dumesh 2010, Colla et al. 2011, Koch et al. 2012, Pyke et al. 2012, Miller-Struttmann and Galen 2014, Williams et al. 2014, Tripoldi and Szalanski 2015).

Monitoring studies on National Forest and BLM lands in southwest Montana have documented sharp declines in some of the largest populations east of the Continental Divide (Shelly 1990; Achuff 1992). One relatively small monitored population was restricted to roadcut habitat and was similarly in decline. Continued declines were projected in the absence of seed germination and recruitment at part or all of the other three sites. Waxing and waning of populations is expected for native ruderal species such as Penstemon lemhiensis.

Fire suppression has been suggested as a factor in the range-wide decline of Lemhi beardtongue (Moseley et al. 1990). It is thought to increase under certain fire regimes, based on qualitative observations after a wildfire in the Salmon National Forest and monitoring of a prescribed burn in Big Hole National Monument, where it increased for a decade after the burn but disappeared from an adjoining untreated area (Heidel and Shelly 1997). Another monitoring study at Badger Pass found that recruitment increased dramatically after fire treatment, consistent with the tendency of fire-adapted species to emerge from seedbanks when fire removes accumulated litter and reduces competition. Based on these studies, prescribed burning has been recommended where Lemhi beardtongue occupies deep-soil rangeland habitats east of the Continental Divide, which are prone to increasing density of Artemisia tridentata in the absence of fire (Heidel and Shelly 2001).

Spotted knapweed is a widespread invader in this species' habitat, particularly west of the Continental Divide. Where Lemhi beardtongue occurs in the Bitterroot National Forest, management is problematic because of the high potential for noxious weeds to expand after fire (Heidel and Shelly 2001). Although herbicides can be used to control invasives, their effect on pollinators of Lemhi beardtongue is unknown. It is an obligate out-crosser, primarily dependent on insect pollination, and relatively small, isolated populations may already be at a disadvantage in their ability to attract effective pollinators (Shelly 1990). Spotted knapweed has not yet invaded populations in Beaverhead and Silver Bow counties, though it has been observed in nearby areas where it can still be controlled without direct impact to this species. Livestock grazing occurs throughout much of the species' range in southwestern Montana, and monitoring transects have been established to assess its effect on populations. The habitat of Lemhi beardtongue was historically impacted by mining at some locations, and renewed gold mining activity could pose a future threat (Shelly 1990).

STATE THREAT SCORE REASON
Reported threats to Montana's populations of Lemhi Beardtongue are those that degrade or destroy its disturbance-dependent habitat (MTNHP Threat Assessment 2021). Noxious plant populations, including severe infestations of Spotted Knapweed (Centaurea stoebe) and Cheatgrass (Bromus tectorum) affect several populations. Chemical herbicide is applied at several populations both to control non-native plants or sagebrush density. Herbicide application likely has negative impacts on Lemhi Beardtongue plants, populations and habitat quality. Livestock trampling and grazing occurs at many populations, and observations indicate that Lemhi Beardtongue flowers are preferred even where diverse forage is available. Fire suppression leading to conifer encroachment is reported at many populations, including one of the most abundant populations. Lemhi Beardtongue requires a natural fire regime, both for habitat maintenance and seed regeneration. Occasional fire is known to increase seed viability, reduce sagebrush canopy, and prevent conifer establishment. Negative impacts from co-occurring threats are potentially amplified by chronic drought, and pose complex management challenges. Concern that prescribed fires at many populations may ultimately lead to noxious plant displacement is credible.