Univ. Calif. Publ. Bot. 32: 297. 1961.
Herbs, 10–30(–70) cm, puberulent on stems immediately distal to nodes, otherwise glabrous; branches usually alternate from distal nodes on short main axis, sometimes whorled from basal nodes, widely spreading. Leaves alternate; stipular glands present at proximal nodes, usually absent distally; blade threadlike to linear, 15–20(–30) × 1–1.5 mm, base flat, not clasping, margins without stalked glands. Inflorescences: cymes dichasial, open, internodes long, flowers widely scattered; bract margins without prominent glands. Pedicels (2–)10–12 mm, to 40 mm in fruit, spreading at 45–90° angle, not or only slightly bent at apex. Flowers: sepals all or outer 2 spreading, not reflexed at tip, lanceolate, 1.5–2(–3) mm, ± equal, marginal glands minute or absent, surfaces glabrous; petals horizontally widely spreading, bright yellow fading white, tinged with orange or red along veins, oblanceolate to obovate, (2–)3–4 mm, apex acute or apiculate; cup yellow, rim lobed between filaments and petal attachments; stamens exserted; filaments 2–3(–3.5) mm; anthers yellow, dehisced anthers 1.2–1.5 mm; ovary chambers 4; styles 2(–3), yellow, 2–3.5 mm, exserted. 2n = 34.
Phenology: Flowering May–Jul.
Habitat: Rocky slopes, chaparral in Pinus sabiniana belt, serpentine soils.
Elevation: 60–1000 m.
Hesperolinon bicarpellatum grows in the southern part of the Inner North Coast Ranges of Lake and Napa counties. Plants in the northern part of its range consistently have two carpels; those in the southern part occasionally may also have three carpels, and sometimes both conditions occur on one plant.