Trifolium microcephalum

Herbs annual, 3–55 cm, densely to sparsely pubescent. Stems erect to ascending, branched. Leaves palmate; stipules obliquely ovate, 0.4–1.2 cm, margins entire or slightly serrate, apex acuminate; petiole 1–5 cm; petiolules 0.5 mm; leaflets 3, blades oblanceolate, obovate, or obcordate, 0.4–1.7 × 0.3–1.1 cm, base cuneate, veins fine or slightly thickened, margins setose, often dentate distally, apex usually retuse, rarely rounded, surfaces villous. Peduncles 1–8 cm. Inflorescences axillary or terminal, 10–40-flowered, globose, 0.5–1.3 × 0.4–1.2 cm; involucres flattened or bowl-shaped, 0.4–1 cm, when folded, nearly completely hiding calyces, villous, incised 1/2 their length, lobes 5–12, lanceolate-ovate, entire or slightly toothed proximally, acuminate. Pedicels absent; bracteoles absent. Flowers 4–6 mm; calyx campanulate-tubular, 3–5.5 mm, pubescent, veins 10, tube 1.8–2.5 mm, lobes ± equal, triangular-aristate, margins hyaline, wavy, orifice open; corolla white or pink to lavender, 4–6 mm, banner oblong, 3–6 × 1–2 mm, apex emarginate. Legumes broadly ellipsoid, 1.5–2 mm. Seeds 1, yellow, reddish mottled, oblong, 1.5 mm, smooth. 2n = 16.

Phenology: Flowering Mar–Jul.
Habitat: Meadows, roadsides, stream banks, forest clearings, grassy slopes.
Elevation: 0–2500 m.

B.C., Alaska, Ariz., Calif., Idaho, Mont., Nev., Oreg., Wash., Mexico (Baja California).

Discussion

Trifolium microcephalum is common in much of its range in California and northward into Oregon, and is rare in much of the rest of its range. It is closely allied with the Chilean T. vernum Philippi (N. W. Ellison et al. 2006), which it resembles greatly, and from which it is distinguished by its shorter calyx lobes (M. Zohary and D. Heller 1984).

Selected References

None.

Lower Taxa