Herbs perennial, 10–40 cm, gla­brous; rhizomes elongate. Stems erect, ascending, or decumbent, branched. Leaves palmate; stipules ovate to lanceolate, 1.5–2 cm, margins entire (proximal stipules) or lacerate (distal stipules), apex acute to acuminate; petiole 1–11 cm; petiolules 0.5 mm; leaflets 3, blades obovate to elliptic, 0.4–4.2 × 0.2–1.3 cm, base cuneate or rounded, veins fine or thickened distally, margins spinulose-serrate, apex usually acute to rounded, sometimes retuse or mucronate, surfaces glabrous. Peduncles 1.5–11 cm. Inflorescences axillary or terminal, 20–50-flowered, subglobose or globose, 1.8–2.5 × 2–2.5 cm; involucres broadly bowl-shaped, 12–20 mm, incised 1/3–1/2 their length, lobes 10+, sharply and acutely serrate, veins prominent. Pedicels straight, 1.5–2 mm; bracteoles linear or ovate, 1–2 mm. Flowers 12–14 mm, odor somewhat unpleasant; calyx whitish, tubular, 5–6 mm, glabrous, veins 10, tube 2–3 mm, lobes green to purple, subequal, abaxial rarely longer than tube, orifice open; corolla usually magenta to purple, rarely white or bicolored, 10–12 mm, banner ovate-oblong, 12–14 × 2–3 mm, apex truncate or rounded, slightly retuse. Legumes oblong, 2–4 mm. Seeds 3 or 4, brown, sometimes mottled, subglobose or mitten-shaped, 1.5 mm, smooth. 2n = 16, 32.

Phenology: Flowering Mar–Sep.
Habitat: Saline flats, beaches, meadows, grassy areas, alluvial soils.
Elevation: 0–2700 m.

Distribution

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B.C., Ariz., Calif., Colo., Idaho, Nev., N.Mex., Oreg., Utah, Wash., Wyo., Mexico (Baja California).

Discussion

Trifolium wormskioldii is largely tetraploid and is widespread in western North America. Distinguishing T. wormskioldii from closely allied species (especially T. mucronatum) is sometimes difficult, which led R. C. Barneby (1989) to synonymize T. mucronatum and T. pinetorum under the former name. Trifolium wormskioldii produces long, white rhizomes; T. mucronatum produces only short rhizomes at most, often only small, fibrous roots or taproots (J. M. Gillett 1980). The distinction of T. pinetorum from T. wormskioldii was supported by N. W. Ellison et al. (2006); those authors did not include material of T. mucronatum in their DNA analyses.

Trifolium wormskioldii rhizomes may have been a food resource for Native American groups in the Pacific Northwest (N. J. Turner and H. V. Kuhnlein 1982).

Selected References

None.

Lower Taxa

None.