| | 1. Pistillate chaff scales thick and hard only near midvein, tip ± flat to concave, projected inward from near top of scale, wing prominent, ovate; receptacle 1.2–1.8 × > wide; disk flowers 4-lobed, pappus bristles 1–5; disk chaff present |
| M. amphibolus |
| | 1' Pistillate chaff scales thick and hard throughout, tip ± cylindric, projected upward from inner edge of scale, wing obscure, ± linear; receptacle not > wide; disk flowers 5-lobed, pappus bristles 0 or 1; disk chaff 0 |
| M. californicus |
| | 2. Longest chaff scale 3–4 mm, wool dense, loose |
| var. californicus |
| | 2' Longest chaff scale 2–3 mm, wool thin, ± appressed |
| var. subvestitus
|