Muhlenbergia 1: 5. 1900.
Annuals 5–37 cm. Stems ascending to erect, branched, sometimes simple, glabrous, sometimes minutely pubescent distally. Leaves: petiole 0–15 mm; proximal cauline leaves simple, margins usually crenate, medial cauline leaves tripartite, segments narrowly elliptic to lanceolate or linear, margins entire or serrate; surfaces sparsely pilose adaxially, abaxially along midvein, and along margins, sometimes glabrous. Racemes: flowers 1–3 per node; bracts elliptic to lanceolate or deeply tripartite, segments narrowly elliptic to lanceolate, margins entire or crenate to serrate. Pedicels 8–16 mm, sparsely glandular-hairy distally, sometimes glabrous or glabrate. Flowers: calyx subrotate to campanulate, lobes triangular to oblong, 0.5–1.5 × 0.4–1 mm; lateral lobes of abaxial lip not closely associated with medial lobe, widely spreading and closely associated with lobes of adaxial lip; corolla 2–2.5 × 2–4 mm; style 1.5–2.5 mm. Capsules 1.5–3 × 1.5–2 mm. Seeds 2, 1.6–2 × 0.8–1 mm.
Phenology: Flowering Mar–Jun.
Habitat: Moist, shaded canyons, moist open coniferous and deciduous forests, talus slopes.
Elevation: 20–1600 m.
B.C., Calif., Oreg., Wash.
Tonella tenella occurs from San Benito County, California, and the High Sierra Nevada north to Washington mostly in the Cascade and Coast ranges but extending eastward through the Columbia River Gorge. Disjunct populations occur in central Oregon, and on Saltspring Island and Mount Tzouhalmen on Vancouver Island in southwestern British Columbia.