Ethnobotany. Lomatium macrocarpum has been used as a food or as medicine by the following First Peoples: Blackfoot, Crow, Flathead, Okanagan-Colville, Paiute, Pomo, Sanpoil, Shuswap and Thompson.

Recent researches. Lomatium macrocarpum contains coumarins and chromones. «Roots of Lomatium macrocarpum (Hook. and Arn.)C. and R. yielded osthol(7-methoxy-8-(3-methyl-2-butenyl)-coumarin) and a chromone, 2-methyl-5-hydroxy-6(3-methyl-2-butenyl)-7-methoxychromone, identified spectroscopically and by synthesis. The serial parts of the plant also contained this chromone along with sibiricin (5,7-dimethoxy-8-(3-methyl-2,3-epoxybutyl)-coumarin) and a new coumarin named macrocarpin. By spectroscopy and chemical degradation macrocarpin was shown to be 7-methoxy-8-(3-methyl-4-(2-methyl-cis-2-butenoyloxy)-cis-2-butenyl)coumarin. These products were not found in four other Lomatium species examined.» in “Coumarins and Chromones from “Lomatium macrocarpum”. Steck,Warren. 1973.

Description by the Jepson. Plant 1–5 dm; taproot or sometimes tubers slender or basally swollen; herbage gray, generally tomentose to densely short-hairy. Stem very short; base not fibrous. Leaf: petiole 1.5–7 cm; blade 2.5–15 cm, oblong to obovate, pinnately or ternate-pinnately dissected, segments 1–7 mm, linear to oblong, entire; cauline leaves like basal. Inflorescence generally tomentose; peduncle 0.5–3 dm; involucel 1-sided; bractlets several, = to > flowers, linear-lanceolate to ovate, acute, ± fused, reflexing, not scarious; rays 5–25, 1–8.5 cm, spreading-ascending; pedicels 1–14 mm. Flower: corolla white, pale yellow, or purplish; ovary generally hairy. Fruit 9–20 mm, lanceolate or oblong to narrowly elliptic, minutely hairy to nearly glabrous; wings generally < body in width; oil tubes per rib-interval 1–3. Chromosomes: 2n=22. Ecology: Rocky (often serpentine) slopes in chaparral or woodland. Elevation: 150–3000 meters. Bioregional distribution: North Coast, Klamath Ranges, Cascade Range, Sierra Nevada Foothills, Tehachapi Mountain Area, San Francisco Bay Area, South Coast . Distribution outside California: to British Columbia, c Canada, ND, Utah.