Plants acaulescent or subacaulescent.
Roots globose tubers with slender taproots at base and elongate upper section < 1 cm, or irregularly thickened tubers abruptly tapered to caudex, or elongate and slender taproots.
Caudices simple or 2–3-branched; basal leaf sheaths from previous years absent or weathering into a few fibers or sparsely chartaceous or chaffy thatch at base of pseudoscape.
Stems absent or < 2 cm; pseudoscapes 0.5–2 cm, subterranean, obscured by leaf sheaths.
Basal leaves glabrous, glabrate or sparsely villous, pubescent, or puberulent; primary leaflets pinnate, 3–6 secondary leaflet pairs along each rachis, laterals at least half central primary in length; secondaries pinnate or pinnatifid; tertiaries entire or pinnatifid (2–6-lobed); ultimate apical lobes linear, oblong, elliptic, 0.7–3 × 0.5–1.5 mm, tips subacute or rounded, mucronulate or not.
Cauline leaves 0–1, similar to basal.
Inflorescences peduncles 1–4, 7–15 cm, glabrous; involucral bracts 0; rays 1–6, 0.5–4 cm, glabrous; involucel bractlets 4–7, disk-like or when separate linear, elliptic, or lanceolate, bractlets fused into an incomplete, involucellar disk, disk segments formed from fusion of 2–12 bracts, tips 2–12-toothed, each segment cleft nearly to base, 2–4 segments per umbellet, sometimes with 2–5 bractlets separate, cleft to near base and 2–6 bractlets fused into 2–3-toothed segments, 1–3 × 0.5–5 mm, margins scarious; umbellets 10–20-flowered; pedicels 0.5–2 mm.
Flowers petals ochroleucous or yellow; anthers ochroleucous or yellow.
Fruits oval, ovate, or elliptic, 6–10 mm, glabrous, glabrate, or puberulent; body 2–3 mm wide; wings 0.5–1 mm, thin; vittae 1–4 in intervals, 6 on commissure.
2n=22.
Open gravelly sites and rocky flats in grasslands, scrublands, woodlands, basalt-derived substrates. Flowering Mar–May. 700–1100 m. ECas, Lava. WA. Native.
Populations from the southwestern part of the range of Lomatium watsonii with glabrous fruit have been called L. frenchii. These populations are found along the ecotone between the Eastern Cascades Slopes and Foothills ecoregion and the Blue Mountains and Columbia Basin ecoregions. There are likely glabrous populations in the far edge of the Eastern Cascades Foothills ecoregion in Washington also. These populations appear to grade imperceptibly into the pubescent L. watsonii populations in the Columbia Basin. Further population-level morphological investigation along this ecotone might result in evidence warranting the delimitation of L. frenchii as a variety of L. watsonii.