| | 1. Plant 5–15(20) cm; leaves generally basal, 1.5–6 cm; inflorescence raceme; pedicel recurved in fruit — alpine |
| T. alpinum |
| | 1' Plant 40–200 cm; leaves basal, cauline, 4–46 cm; inflorescence generally panicle; pedicel ± erect in fruit |
| |
| | 2. Flower bisexual; anther tip obtuse, filament flat; fruit body generally semi-circular to crescent-shaped |
| T. sparsiflorum |
| | 2' Flower unisexual; anther tip abruptly pointed, filament thread-like; fruit body obliquely ovate to fusiform or ± circular to obovate |
| |
| | 3. Fruit mostly reflexed, body slightly compressed laterally, ribs generally 3 per side, ± straight; n North Coast, nw Klamath Ranges |
| T. occidentale |
| | 3' Fruit spreading to ascending, body compressed laterally throughout or only near margins, ribs 1–3 per side, ± curved; California Floristic Province (except Great Central Valley, Channel Islands), Great Basin Floristic Province |
| T. fendleri |
| | 4. Fruit body ± compressed laterally throughout, side with 2–3 ribs, 0 veins, obliquely ± ovate to ± obovate; lower surface of upper leaves generally finely glandular-puberulent (at 20×) |
| var. fendleri |
| | 4' Fruit body compressed laterally generally only near margins, side with generally 1 rib, several wavy veins, obliquely and ± widely obovate to ± circular; lower side of upper leaves generally glabrous |
| var. polycarpum
|