| | 1. Calyx tube hairs appressed, not hooked |
| |
| | 2. Corolla limb 2–5 mm diam; calyx tube ± = or < lobes; style < nutlets; stem often decumbent but base not stolon-like; annual, biennial, short-lived perennial herb |
| M. laxa |
| | 2' Corolla limb 5–10 mm diam; calyx tube >> lobes; style ± = or > nutlets; stem base often creeping or stolon-like; perennial herb |
| M. scorpioides |
| | 1' Calyx tube hairs spreading, some or all hooked |
| |
| | 3. Calyx lobes ± unequal; corolla white, limb 1–2 mm diam |
| M. verna |
| | 3' Calyx lobes ± equal; corolla generally blue (sometimes initially yellowish) or pink; limb 1–10 mm diam |
| |
| | 4. Corolla limb 5–10 mm diam; pedicel in fruit > or = calyx; perennial herb |
| M. latifolia |
| | 4' Corolla limb 1–5 mm diam; pedicel in fruit < to << calyx; annual, winter annual, or biennial |
| |
| | 5. Flowers ± restricted to upper half of plant; hairs on lower leaf surface straight; style = or > nutlets |
| M. discolor |
| | 5' Flowers ± from base of plant; hairs on lower leaf surface hooked; style << nutlets |
| M. micrantha
|