Herbs annual, 5–45 cm, sparsely villous to glabrescent. Stems prostrate, decumbent, or erect, branched. Leaves pal­mate; stipules ovate, 0.4–1.2 cm, margins serrate-lacerate, apex acuminate; petiole 1–4 cm; petiolules 0.5 mm; leaflets 3, blades obovate, 0.5–1.5 × 0.4–1 cm, base cuneate, veins moderately prom­inent, margins denticulate, apex truncate, retuse, or mucronulate, surfaces glabrescent. Peduncles 1.5–4 cm. Inflorescences axillary or terminal, 2–15-flowered, sub­globose, 1.5–1.8 × 0.5–1.5 cm; involucres flattened or vase-shaped, 1–3 mm, when folded, not hiding flowers except proximally, incised 2/3–3/4 their length, lobes 5–15, linear-lanceolate, entire, acuminate. Pedicels erect, 1.5 mm; bracteoles absent. Flowers 8–11 mm; calyx campanulate-tubular, not slit between adaxial lobes, 6–9 mm, usually densely pubescent, rarely sparsely so, veins 10, tube 2.5–4.5 mm, lobes unequal, lanceolate-subulate, orifice open; corolla light purple with darker purple keel petals, 6–10 mm, banner narrowly obovate, 4–5 × 1 mm, apex retuse. Legumes sessile, oblong, 5 mm. Seeds 3–6(–9), pale brown, mottled purple, globose to mitten-shaped, 0.8–1 mm, smooth to slightly roughened, semiglossy.

Phenology: Flowering Apr–May.
Habitat: Sandy, rich soils in open Monterey pine forests, often after fire.
Elevation: 0–50 m.

Distribution

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Calif.

Discussion

Trifolium trichocalyx is an extremely rare species known only from Mendocino and Monterey counties. D. I. Axelrod (1982) suggested that T. trichocalyx might have originated as a hybrid between T. microcephalum and T. variegatum, but this is not supported by molecular studies (N. W. Ellison et al. 2006). It appears to be fire-adapted and appeared in large numbers shortly after a fire in 1987 (U.S. Fish and Wildlife Service 2004).

Selected References

None.

Lower Taxa

None.