| 1 | Flowering stems without cauline leaves; inflorescence apparently lateral, exceeded by a subulate bract |
| 1' | Flowering stems with cauline leaves; inflorescence apparently terminal, not exceeded by bracts |
| 8 | Small annuals; leaves and flowering stems distinct; inflorescence consisting of one or more dense heads |
| 8' | Robust rhizomatous or caespitose perennials; leaves and flowering stems closely similar |
| 9 | Stems with interrupted pith, glaucous, with 12-18 prominent longitudinal ridges, not very rigid or pungent; perianth-segments narrow, lanceolate-acuminate |
| 9' | Stems with continuous pith, not glaucous or prominently ridged, very rigid and pungent |
| 10 | Flowers greenish or straw-coloured; perianth-segments narrowly ovate- or elliptic-acuminate, the inner without hyaline apical auricles |
| 10' | Flowers brownish or fuscous; perianth-segments ovate-apiculate, the inner with hyaline apical auricles |
| 11 | Flowers in dense glomerules; anthers a little longer than filaments; capsule equalling or shorter than perianth-segments |
| 11' | Flowers not in dense glomerules; anthers much longer than filaments; capsule distinctly exceeding perianth-segments |
| 12 | Capsule 3 mm or more wide, clearly exceeding the persistent perianth; stems very rigid and pungent, 3-5 mm diam. |
| 12' | Capsule less than 3 mm wide, scarcely exceeding the perianth |
| 13 | Capsule acute, 1.5-2 mm wide; stems slender, 1.5-2 mm diam. |
| 13' | Capsule obtuse, apiculate, 2-2.5 mm wide; stems 2.5-3 mm diam. |
| 2 | Leaves with transverse walls (septate) |
| 2' | Leaves without transverse walls (not septate) |
| 3 | Perianth-segments 3-4 mm long; flowers in dense, echinate glomerules; capsule clearly exceeding perianth-segments, distinctly rostrate |
| 3' | Perianth-segments c. 2.5 mm long; flowers in dense, rounded glomerules; capsule slightly exceeding perianth-segments, not rostrate |
| 4 | Robust rhizomatous perennials; stems 30-120 cm high |
| 4' | Slender annuals; stems generally less than 30 cm high |
| 5 | Capsule broadly oblong-ovoid or subglobose, 2 x 1.5 mm; perianth-segments 2-2.5 mm long |
| 5' | Capsule oblong-ellipsoid, 3-4.5 mm long; perianth-segments 3.5-6 mm long |
| 6 | Inner perianth-segments obtuse or shortly acute, generally shorter than the capsule |
| 6' | Inner perianth-segments acuminate, exceeding the capsule |
| 7 | Flowers solitary or occasionally 2-3 together, spaced along the inflorescence-branches; seeds distinctly striate-reticulate |
| 7' | Flowers generally in dense, fan-shaped glomerules; seeds almost smooth |
