| | 1. Stems unarmed (leaves not forming spines) |
| |
| | 2. Flowers generally 6–7; pappus 0 (but fruit covered with long, pappus-like hairs); axillary leaf clusters generally 0 |
| 2 T. comosa |
| | 2' Flowers 4(5); pappus present; axillary leaf clusters generally present |
| |
| | 3. Main leaves densely tomentose or silvery; clustered leaves ± (ob)lanceolate |
| T. canescens |
| | 3' Main leaves glabrous or sparsely tomentose; clustered leaves narrowly linear |
| |
| | 4. Main leaves narrowly awl-shaped, stiffly ascending or appressed, generally 5–10 mm; clustered leaves generally 3–10 mm, glabrous; fruit generally 3–4 mm, short-stiff-hairy; pappus of ± 100 bristles |
| T. glabrata |
| | 4' Main leaves ± thread-like, soft, generally 10–30 mm; clustered leaves generally 10–20 mm, loosely tomentose; fruit 5–6 mm, long-soft-hairy; pappus of ± 20 stiff bristles or slender scales (± hidden by fruit hairs) |
| T. tetrameres |
| | 1' Stems armed with spines derived from main leaves |
| |
| | 5. Fruit glabrous, 2.5–3.5 mm |
| T. argyraea |
| | 5' Fruit ± long-soft-hairy, 4–8 mm |
| |
| | 6. Main leaves narrowly (ob)lanceolate, finally deciduous, base not hardened; pappus 0 |
| 2 T. comosa |
| | 6' Main leaves tapered to tip, persistent as stout spines, base expanded, hardened; pappus present |
| |
| | 7. Clustered leaves silvery-hairy; fruit ± short-hairy; pappus of many fine bristles 9–12 mm |
| T. stenolepis |
| | 7' Clustered leaves ± glabrous; fruit densely long-hairy; pappus of ± 25 slender scales 6–9 mm |
| |
| | 8. Spines sharply recurved, < 2 cm, tomentose; involucres generally 8–12 mm, bell-shaped; fruit generally 6–8 mm |
| T. spinosa |
| | 8' Spines straight, generally 2–4 cm, becoming glabrous; involucres generally 7–9 mm, obconic; fruit generally 4–5 mm |
| T. axillaris |
| | 9. Phyllaries and peduncles glabrous; fruit hairs generally 6–8 mm |
| var. axillaris |
| | 9' Phyllaries and peduncles tomentose; fruit hairs generally 9–11 mm |
| var. longispina
|