| | 1. Bractlets subtending calyx 1–9 mm wide |
| |
| | 2. Flower clusters weakly defined, not subtended by bracts, arrayed in panicle-like inflorescence — South Coast Ranges (Salinas Valley) |
| M. abbottii |
| | 2' Flower clusters dense, subtended by bracts, arrayed in head-, spike-, or panicle-like inflorescence |
| |
| | 3. Inflorescence spike- or narrowly panicle-like, clusters congested or well separated; Inner South Coast Ranges, Peninsular Ranges |
| M. aboriginum |
| | 3' Inflorescence head-like (sometimes with a few lower clusters); sw Central Western California |
| M. palmeri |
| | 1' Bractlets subtending calyx < 1 mm wide |
| |
| | 4. Calyx lobes < or ± = tube, length generally ± 1.5 × width; bractlets generally < half calyx length |
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| | 5. Calyx sparsely bristly (some hairs 1–3 mm); flower clusters dense, often well separated in naked, spike-like inflorescence — Peninsular Ranges, w Sonoran Desert |
| 2 M. densiflorus |
| | 5' Calyx densely hairy (not bristly); flower clusters dense or open, in spike- to panicle-like inflorescence |
| |
| | 6. Leaf blade 5–20 cm, thick, upper surface generally densely hairy, tawny, sinuses closed, lobes overlapping; branches generally stout; Outer South Coast Ranges, South Coast |
| M. davidsonii |
| | 6' Leaf blade 2–6(11) cm, thin, upper surface generally green, sparsely hairy, sinuses open, lobes not overlapping; branches generally slender; Central Western California, Southwestern California |
| M. fasciculatus |
| | 4' Calyx lobes ± = to >> tube, length generally 1.5–3 × width; bractlets generally > half calyx length |
| |
| | 7. Calyx lobes in bud joined by their margins (calyx in bud 5-angled or -winged); calyx lobes in flower widely ovate, their hairs generally tawny, coarse |
| |
| | 8. Calyx sparsely bristly (some hairs 1–3 mm); flower clusters dense, often well separated in naked, spike-like inflorescence; Peninsular Ranges, w Sonoran Desert |
| 2 M. densiflorus |
| | 8' Calyx densely hairy (not bristly); flower clusters dense or open, generally congested in short, basally leafy, spike-like inflorescence; w&c Transverse Ranges |
| M. marrubioides |
| | 7' Calyx lobes in bud not joined by their margins (calyx in bud not angled or winged); calyx lobes in flower narrowly triangular to ovate, their hairs white to grayish, soft |
| |
| | 9. Petals white; leaf lobes 3–5, obvious; leaf upper surface becoming glabrous, dark green — s Channel Islands |
| M. clementinus |
| | 9' Petals light purple; leaf lobes 0 or obscure; leaf upper surface hairy, white or green |
| |
| | 10. Branches generally coarse, stiff; flower clusters generally densely many-flowered, arrayed in spike- to panicle-like inflorescence; leaves 4–6(11) cm; widespread |
| M. fremontii |
| | 10' Branches slender, flexible; flower clusters loosely 3–6-flowered, generally arrayed in panicle-like inflorescence; leaves 2.5– 4.5(7) cm; Outer South Coast Ranges |
| M. jonesii
|