| | 1. Terminal bud covered with scales; petals generally 0; style exserted (subg. Rhamnus) |
| |
| | 2. Leaves deciduous; sepals 5; fruit black, 3-stoned |
| R. alnifolia |
| | 2' Leaves evergreen; sepals 4; fruit red, 2-stoned (R. crocea complex) |
| |
| | 3. Leaf blade < 15 mm, flat; branches spreading |
| R. crocea |
| | 3' Leaf blade > 15 mm, lower side concave; branches generally ascending |
| |
| | 4. Leaf blade elliptic; small tree; Channel Islands |
| R. pirifolia |
| | 4' Leaf blade ovate to round; shrub; mainland |
| |
| | 5. Branches stiff, twigs glabrous to densely hairy; California Floristic Province, Desert Mountains |
| R. ilicifolia |
| | 5' Branches flexible, twigs densely hairy; Peninsular Ranges |
| R. pilosa |
| | 1' Terminal bud not covered with scales; petals present; style including (subg. Frangula) |
| |
| | 6. Leaves thin, deciduous |
| |
| | 7. Fruit 3-stoned; leaf blade 50–150 mm, generally > 80 mm |
| R. purshiana |
| | 7' Fruit 2-stoned; leaf blade 15–80 mm |
| R. rubra |
| | 6' Leaves thick, generally evergreen (R. californica complex) |
| |
| | 8. Leaf blade ± glabrous on lower side |
| R. californica |
| | 9. Fruit 2-stoned; blade dark green on upper side, bright green or yellow on lower |
| subsp. californica |
| | 9' Fruit 3-stoned; blade ± equally yellow on both sides |
| subsp. occidentalis |
| | 8' Leaf blade tomentose on lower side |
| R. tomentella |
| | 10. Leaf margin entire or with blunt teeth |
| |
| | 11. Leaf blade widely elliptic; s Klamath Ranges, Inner North Coast Ranges |
| subsp. crassifolia |
| | 11' Leaf blade narrowly elliptic; widespread |
| subsp. tomentella |
| | 10' Leaf margin with sharp teeth |
| |
| | 12. Leaf margin dentate to dentate-serrate; c&s Sierra Nevada, Tehachapi Mountain Area, Transverse Ranges, Peninsular Ranges, San Jacinto Mountains |
| subsp. cuspidata |
| | 12' Leaf margin serrate to ± entire; Desert Mountains |
| subsp. ursina
|