| | 1. Fruit strongly 5-ribbed, < 3 mm wide, generally with prominent warts or coarse wrinkles between ribs; involucre in fruit enlarged, brown, papery |
| |
| | 2. Leaf ± sessile, ± linear |
| |
| | 3. Perianth bright red, 3–4 × length of involucre in flower |
| M. coccinea |
| | 3' Perianth pale pink to magenta, ± 2 × length of involucre in flower |
| M. linearis var. linearis |
| | 2' Leaf obviously petioled, blade lanceolate or wider |
| |
| | 4. Involucre in flower short-hairy at base, glabrous on lobes, in fruit 10–15 mm |
| M. nyctaginea |
| | 4' Involucre in flower hairy throughout on outside, in fruit generally < 8 mm |
| |
| | 5. Stem branched generally near top, ascending to erect, generally glabrous (or finely strigose) in lower half; leaf length > width, tip generally acute |
| M. oblongifolia |
| | 5' Stem much-branched from near base, decumbent to ascending, hairy or glandular throughout; leaf length generally = width, tip obtuse to acute |
| M. pumila |
| | 1' Fruit smooth to moderately 5- or 10-ribbed or -angled, often > 3 mm wide, sometimes with low wrinkles or warts; involucre in fruit little changed |
| |
| | 6. Flowers 3–16 per involucre, bracts either > 22 mm or free |
| |
| | 7. Perianth ± 15 mm; involucral bracts 15–30 mm, free to fused ± 1/2 length |
| M. alipes |
| | 7' Perianth 40–60 mm; involucral bracts > 22 mm, fused > 1/2 length |
| |
| M. greenei |
| | 8' Fruit not angled, often with 10 lines or low ribs |
| M. multiflora |
| | 9. Involucral bracts obtuse; fruit warty, gelatinous when wet |
| var. glandulosa |
| | 9' Involucral bracts acute; fruit smooth or lightly warty with 10 slender, tan ribs; not gelatinous when wet |
| var. pubescens |
| | 6' Flower 1 per involucre; bracts < 15 mm, fused |
| |
| | 10. Perianth 30–50 mm; fruit bluntly 5-ribbed, cross-wrinkled |
| M. jalapa |
| | 10' Perianth < 15 mm; fruit not 5-ribbed |
| |
| | 11. Involucre > 10 mm, lanceolate lobes > tube; perianth white; leaves ascending |
| M. tenuiloba |
| | 11' Involucre < 10 mm, ± ovate lobes < tube; perianth white to magenta; leaves widely spreading |
| |
| | 12. Perianth pink to purple-red; leaf puberulent or glandular-hairy (youngest leaves with conic-based hairs); fruit generally very lightly dotted or wrinkled, sometimes smooth |
| M. californica |
| | 12' Perianth white to pale pink; leaf finely glandular-hairy; fruit generally lightly dotted or wrinkled |
| M. bigelovii |
| | 13. Fruit ovoid, lines 0 or inconspicuous; stems and leaves glandular-hairy |
| var. bigelovii |
| | 13' Fruit ± spheric, generally with 10 pale lines; stems and leaves with short, reflexed hairs, generally also ± glandular |
| var. retrorsa
|