Montana Field Guide

Plants: Cup Clover is a hairless annual herb with ascending or erect stems which stand 1-5 dm tall (Hitchcock 1961).

Leaves: Small "3-leaf clover" leaves are borne alternately on the stems, each leaf having 2 lanceolate stipules (appendages), 4-10 mm long (Lesica 2012), at the base of a long petiole (stalk) which bears 3 broadly oblanceolate leaflets; leaflets 5-25 mm long, with fine spiny-toothed margins much of their length (Hitchcock 1961).

Inflorescence: Clover heads are borne on leafless peduncles (stalks which support an inflorescence, in this case, racemose) from leaf axils. Each head consists of 5-30 flowers nestled within a spreading to somewhat deeply cupped, prominently veined saucer-like involucre (a whorl of bracts which subtend an inflorescence) with 6-15 shallow, finely bristled lobes that are fused together; the heads are 5-15 mm long and about the same width (Hitchcock 1961).

(Lesica’s contribution adapted from Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX)

Flowers late May-August, subject to elevational differences (Barneby et al. 1989).

This species is distinguished from other Montana Trifolium species by the combination of its annual habit, flower heads subtended by a shallowly-lobed, glabrous involucre, and lower calyx teeth with 2-3 bristle-tips (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Wet meadows, sandy streambanks, roadsides; valleys, montane (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

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 frigidus, Bombus huntii, Bombus melanopygus, Bombus mixtus, Bombus nevadensis, Bombus rufocinctus, Bombus sylvicola, Bombus ternarius, Bombus occidentalis, Bombus pensylvanicus, Bombus bimaculatus, Bombus griseocollis, Bombus impatiens, Bombus insularis, Bombus suckleyi, Bombus bohemicus, Bombus flavidus, and Bombus kirbiellus (Plath 1934, Hobbs 1966, Macior 1974, Heinrich 1976, Bauer 1983, Thorp et al. 1983, Mayer et al. 2000, Rao and Stephen 2007, Wilson et al. 2010, Colla and Dumesh 2010, Colla et al. 2011, Koch and Strange 2012, Koch et al. 2012, Miller-Struttmann and Galen 2014, Williams et al. 2014).

Flowers: The small flowers are about 2-5 mm long and have bilateral symmetry. The calyx has a 13- to 20-nerved tube and 5 teeth; the teeth are usually somewhat longer than the tube, the lower 3 each having 2 or 3 bristle-like tips. The white, cream, or pink corolla is about as long as the tips of the calyx teeth, and consists of a banner (the large, hooding, upper segment), the wings (the side segments) and a keel (the prow-shaped bottom segment) (Hitchcock 1961).

Fruit: The fruit is a pod, typically with 2 seeds (Hitchcock 1961).

STATE THREAT SCORE REASON
Threat impact not assigned because threats are not known (MTNHP Threat Assessment 2021).