Leaves opposite or appearing whorled because of the presence of short axillary leafy shoots; stipules conspicuous, scarious.
Inflorescence a terminal cyme; pedicels longer than or rarely equal to the sepals. Sepals 5, free. Petals white to pink, entire. Stamens 2–10. Styles 3. Ovary 1-locular.
Capsule ovoid, opening by 3 valves; seeds numerous, with or without a scarious wing.
| | Key to the species | |
| 1 | Plant perennial with usually thick, woody taproot; stipules usually more than 4 mm long | 2 |
| Plant annual, biennial or rarely short-lived perennial with ± slender taproot; stipules rarely more than 4 mm long | 9 |
| 2 | Mature seeds yellow-brown to dark grey-brown | 3 |
| Mature seeds jet-black
Back to 1 | 8 |
| 3 | Plant completely glabrous; seeds scariously winged, the wings deeply erose-laciniate | Spergularia levis |
| Plant with at least the inflorescence glandular-hairy; wings of seeds, if present, entire to erose denticulate, never deeply erose-laciniate
Back to 2 | 4 |
| 4 | Leaves mostly prominently caudate; capsules usually 3.5–5.5 mm long; seeds mostly 0.4–0.6 mm long (excluding wing) | 5 |
| Leaves acute to mucronate or shortly caudate; capsules up to 9 mm long; seeds mostly 0.6–1.1 mm long (excluding wing)
Back to 3 | 6 |
| 5 | Branches usually erect from base, occasionally decumbent; inflorescences few-flowered, with sparse to dense glandular hairs; sepals often with dark purple basal spots or marginal striae; stamens (5–)6–8; seeds mostly very dark grey-brown to jet-black, distinctly metallic-iridescent | Spergularia brevifolia |
| Branches consistently decumbent from base; inflorescences many-flowered, with dense glandular hairs; sepals with purplish spots obscure or usually absent; stamens (5–)10; seeds dark purple-, grey- or blackish-brown but never jet-black or metallic-iridescent, usually rugulose-colliculate
Back to 4 | Spergularia rubra |
| 6 | Sepals usually 2.5–4 mm long; stamens usually 2–5; mature seeds usually 0.6–0.8 mm long (excl. wing), either with fine marginal papillae distinctly paler than testa; or seeds occasionally winged and then marginal papillae absent, often both forms in the same capsule | Spergularia marina |
| Sepals usually 4–7 mm long; stamens usually 5–10; mature seeds usually 0.7–1.1 mm long (excl. wing), smooth to colliculate or papillose, usually all scariously winged
Back to 4 | 7 |
| 7 | Mature seeds almost smooth, bright to dull rust-brown | Spergularia media |
| Mature seeds colliculate-papillose, dark grey-brown
Back to 6 | Spergularia tasmanica |
| 8 | Stipules acute to scarcely acuminate; petals 4 mm long, shorter than sepals; capsules 6–9 mm long; seeds usually 0.7–0.9 mm long (excl. wing), colliculate-papillose, usually scariously winged | Spergularia tasmanica |
| Stipules mostly long-acuminate; petals 2.5–5 mm long, about equal to sepals; capsules (3–) 4–6 mm long; seeds usually 0.5–0.6 mm long, coarsely blunt-papillose, rarely ± smooth, wingless
Back to 2 | Spergularia brevifolia |
| 9 | Mature seeds usually pale olive-brown or rust-brown, metallic-iridescent lustre usually lacking or obscure, smooth to finely papillose | 10 |
| Mature seeds grey-brown to jet-black, usually with clear metallic-iridescent lustre, or the lustre ± hidden by very densely packed papillae
Back to 1 | 11 |
| 10 | Mature capsules narrow-ovoid, usually 4–6 mm long; mature seeds (0.5–)0.6–0.8(–0.9) mm long, rust-brown or rarely darker, either with fine marginal papillae distinctly paler than testa; or seeds occasionally scariously winged and then papillae absent, often both in the same capsule | Spergularia marina |
| Mature capsules ovoid to subglobose, usually 2–4 mm long; mature seeds 0.35–0.55(–0.6) mm long, pale olive-brown, smooth to finely papillose, with papillae not or scarcely paler than testa, never winged
Back to 9 | Spergularia bocconei |
| 11 | Leaves mostly ± glandular-hairy, rarely glabrous; stipules usually longer than wide, mostly acuminate; petals up to 5 mm long; stamens 6–10, rarely less | 12 |
| Leaves mostly glabrous; stipules often wider than long, usually not acuminate or occasionally so; petals rarely more than 2 mm long; stamens 2 or 3, rarely more
Back to 9 | Spergularia diandra |
| 12 | Leaves mostly prominently caudate; stipules silvery; seeds rugulose-colliculate/tuberculate to papillose | Spergularia rubra |
| Leaves obtuse, mucronate or prominently caudate; stipules not silvery; seeds coarsely blunt-papillose, tuberculate or rarely ± smooth
Back to 11 | 13 |
| 13 | Leaf apex obtuse to mucronulate; stipules (1–)2–3 mm long; seeds narrowly oblique-pyriform to trigonous,0.45 mm long, usually jet-black, metallic-iridescent lustre ± hidden beneath very densely packed, blunt papillae | Spergularia diandroides |
| Leaf apex usually prominently caudate, sometimes obtuse to mucronate; stipules (3–)4–5(–8) mm long; seeds usually broadly pyriform, (0.45–)0.5–0.6(–0.75) mm long, dark grey-brown to jet-black, usually with prominent metallic-iridescent lustre, coarsely blunt-papillose, tuberculate or rarely ± smooth
Back to 12 | Spergularia brevifolia |
