Shasta County Arnica

Arnica venosa is known only from Shasta and Trinity counties.

Plants 20–60 cm. Stems simple or branched (prominently ribbed; caudices woody). Leaves 6–10 pairs, cauline (basal leaves withered by flowering; proximal cauline scalelike, middle leaves largest, distal reduced, bractlike) usually broadly sessile, rarely broadly petiolate; blades (3- or 5-nerved, strongly reticulate-veined) ovate-elliptic to broadly lanceolate, 3–7 × 1.5–4 cm (firm), margins irregularly and coarsely serrate, apices acute to obtuse, faces: abaxial pilose, stipitate-glandular (especially on veins), adaxial glabrate to stipitate-glandular. Heads 1. Involucres turbinate-campanulate. Phyllaries 8–19, ovate to broadly lanceolate. Ray florets 0. Disc florets 30–60; corollas yellow; anthers yellow. Cypselae dark gray, 6–8 mm, densely hirsute (hairs duplex); pappi white, bristles barbellate. 2n = 38.

Arnica venosa H. M. Hall, Univ. Calif. Publ. Bot 6: 174. 1915.
Rootstock creeping; stem simple below, 1-3-branched above, leafy, 3-4.5 dm. high, sulcate, pilose and glandular-puberulent, especially above; lower leaves scale-like, connate and sheathing; stem-leaves opposite, sessile, elliptic or oblanceolate, firm, 4—6 cm. long, 1.5-3 cm. broad, acute or short-acuminate, sharply dentate, or the uppermost entire, 3-5-ribbed, strongly reticulatevenose beneath, sparingly short-pilose; heads solitary at the ends of the stem and leafy branches; involucre turbinate-campanulate, 10-12 mm. high, nearly as broad, pilose; bracts 8-15, linear-lanceolate, acuminate; ray-flowers wanting; disk-corollas light-yellow, conspicuously pilose, 7-8 mm. long; achenes 5 mm. long, hirsute; pappus-bristles white, 10 mm. long, short-plumose.
Type locality: Salt Creek, Shasta County, California. Distribution: Known only from the type locality.

Arnica venosa is a rare California species of flowering plant in the family Asteraceae known by the common name Shasta County arnica. It should not be confused with the Mt. Shasta arnica, A. viscosa.

Arnica venosa is endemic to the Klamath Mountains of northwestern California, where it can be found only in Shasta and Trinity Counties.