| | 1. Branches alternate; perennial herb; leaf veins obscure, blade ovate to narrowly elliptic; flowers generally ± solitary; style branched < 1/3 from tip; fruit 4-grooved (sect. Stegnocarpus) |
| T. canescens |
| | 2. Corolla 4–7.5 mm, at top 2.5–4.5 mm wide |
| var. canescens |
| | 2' Corolla 8–12 mm, at top 5–8 mm wide |
| var. pulchella |
| | 1' Branches opposite; annual or perennial herb; leaf veins obvious, ± sunken, blade ovate, round, or obovate; flowers clustered; style branched 1/2–4/5 from tip; fruit 4-lobed (sect. Tiquiliopsis) |
| |
| | 3. Rhizome present; stem ± glandular; leaf veins deeply sunken, 4–7 pairs; hairs within calyx long |
| T. plicata |
| | 3' Rhizome 0; stem ± non-glandular; leaf veins shallowly sunken, 2–3 pairs; hairs within calyx short or 0 |
| |
| | 4. Annual; style < calyx; leaf margin entire, lateral veins ± 30° from midvein; corolla pink to white; seed oblong-ovoid |
| T. nuttallii |
| | 4' Perennial; style > calyx; leaf margin ± crenate, lateral veins ± 45° from midvein; corolla blue, purple, or lavender; seed spheric |
| T. palmeri
|