Montana Field Guide

PLANTS: Perennial from rhizome-like caudex-branches (Barneby 1964). The root-crown is deeply buried but can become exposed by shifting sand of mobile dunes (Barneby 1964). Plants are densely strigose (Lesica et al. 2012). Stems solitary, lax to ascending, 10–25 cm (Lesica et al. 2012).

LEAVES: 1–12 cm long. Mostly pinnate with 1-7 leaflets; the terminal leaflet is longest and confluent with the rachis (Lesica et al. 2012). Petioles are slender (Barneby 1964). Stipules are lanceolate, 2–6 mm long, and often united basally.

INFLORESCENCE: Racemes of 2-10(25) white to light purple flowers. Racemes with spreading to ascending flowers grow among the leaves (Lesica et al. 2012).

In Montana two varieties are present, filifolius and apus. Refer below to Diagnostic Characteristics and Range Comments.

Astragalus ceramicus is unique in being diffusely cryptophytic (bears its buds below the soil), with confluent terminal leaflets, and an inflated pod that does not lose its red mottling (Barneby 1964). Its pods (fruits) are balloon-shaped, large, and red-mottled.

Variety filifolius has pods that have a stipe of 1-3 mm length and grows in the counties of eastern Montana, adjacent North and South Dakota, and other regions of the Great Plains (McGregor 1986, Flora of the Great Plains). Pods are (2)3-5 cm long and 1.4-2.6 cm in diameter (Barneby 1964). Some lower leaves may have 1-2(3) pairs of lateral leaflets (Barneby 1964).

Variety apus has pods that are sessile to the stem and is endemic to Beaverhead County and adjacent Idaho (Lesica et al. 2012). Pods are 2-4 cm long and about 1.5-2.4 cm in diameter (Barneby 1964). Lateral leaflets are wanting or nearly so (Barneby 1964).

Sand or very sandy soil of sandhills, below sandstone outcrops; plains, valleys, montane (Lesica et al. 2012).

Long distances between occurrences is thought to reduce opportunities for pollen exchange and has led to the perpetuation of small regional differences that consist of many minor races (Barneby 1964). Three varieties have been recognized since at least 1964: ceramicus, apus, and filifolius of which the latter two occur in Montana and are depicted in their own Plant Field Guide accounts.

POLLINATORS
The following animal species have 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 borealis, Bombus centralis, Bombus fervidus, Bombus flavifrons, Bombus huntii, Bombus mixtus, Bombus nevadensis, Bombus rufocinctus, Bombus ternarius, Bombus terricola, Bombus occidentalis, Bombus pensylvanicus, Bombus griseocollis, and Bombus insularis (Macior 1974, Thorp et al. 1983, Mayer et al. 2000, Colla and Dumesh 2010, Wilson et al. 2010, Koch et al. 2012, Miller-Struttmann and Galen 2014, Williams et al. 2014).

Flowers white to light purple; calyx white- and/or black-strigose; sepals 2–3 mm long; banner reflexed, 8–11 mm long; keel 6–8 mm long. Legume ovoid, inflated, 15–40 mm long, maroon-mottled, glabrous, papery, pendent (Lesica et al. 2012).

The removal of natural disturbance regimes, including fire, ungulate grazing and pocket gopher activity, leads to dune stabilization and reduces the extent of early seral blowout vegetation areas upon which this species depends. Painted milkvetch would benefit from restoration of the fire regime and moderate grazing, at least in years following burns. Severe destabilization of the dunes, e.g., from off-road vehicle use, could also threaten its habitat.

Studies have shown that Pottery Milkvetch occurs in early successional habitats that are maintained by grazing or fire. Threats would include any process or action that hinders or prevents grazing or fire; however, the scope, severity, or timing of such threats have not been documented (MTNHP Threat Assessment 2021).

Plants occur in habitats where the potential for off-highway vehicle use is real; however, actual use has not been documented at any known occurrence.

Invasive plants are a potential threat to its habitat though current assessments on the condition of occupied habitats have not been made.

STATE THREAT SCORE REASON
A reported threat to Montana’s populations of Painted Milkvetch includes natural ecological succession of the habitat (MTNHP Threat Assessment 2021). Plants require early successional habitat, which can be maintained by grazing and/or fire. Potential threats to populations could also come from incompatible recreational activities and invasion by non-native plant species is greatly needed (MTNHP Threat Assessment 2021).