Peduncles filiform, often dark-coloured; bracts minute. Sepals 4 [or 5], usually dark-coloured, usually not persistent in fruit. Petals 4 [or 5], involute around paired stamens in bud, usually deep lilac-pink, occasionally paler pink or white, usually not persistent in fruit. Stamens usually 8, hypogynous; anthers 4-locular, basifixed. Ovary compressed; style filiform.
Capsule opening longitudinally; seeds 2–4 mm long, brown and smooth, with fine hairs and an appendage.
| | Key to the species | |
| 1 | Stems winged | Tetratheca juncea |
| Stems not winged | 2 |
| 2 | Plants with dimorphic foliage; some branches glabrous with linear leaves, some with dense, stout, antrorse hairs and broad-elliptic to more or less circular leaves | Tetratheca shiressii |
| Plants with all leaves similar
Back to 1 | 3 |
| 3 | Stems almost completely leafless | Tetratheca subaphylla |
| Stems leafy, at least on the lower part
Back to 2 | 4 |
| 4 | Leaves linear or appearing linear with recurved or revolute margins | 5 |
| Leaves not linear
Back to 3 | 11 |
| 5 | Leaves in whorls of 3–7 | 6 |
| Leaves alternate, occasionally some opposite
Back to 4 | 10 |
| 6 | Peduncles distinctly glandular-hairy | Tetratheca glandulosa |
| Peduncles not obviously glandular-hairy
Back to 5 | 7 |
| 7 | Stems with hairs of 2 types, some minutely spreading or retrorse (and present at least at the nodes) and the others 0.5–1.5 mm long | 8 |
| Stem hairs not as above, and tending to be antrorse
Back to 6 | 9 |
| 8 | Most stem hairs short and conspicuously retrorse | Tetratheca rubioides |
| Stem hairs usually both short and long, but if most short, then these not conspicuously retrorse
Back to 7 | Tetratheca neglecta |
| 9 | Stems bristly with dense pale brown hairs, regularly antrorse; gland-tipped hairs on calyx | Tetratheca ericifolia |
| Stems with hairs sparse to numerous, white or grey, tending to be antrorse but often twisted and irregularly directed, or stems glabrous and tuberculate
Back to 7 | Tetratheca rupicola |
| 10 | Stem terete and ridged with numerous antrorse bristles; fruit depressed-globose | Tetratheca decora |
| Stem terete or ridged and appearing 4-angled and tuberculate with tubercles often produced into minute white hairs, some stout brown bristles also present; fruit often beaked, obovate to obcuneate or cordate, turgid
Back to 5 | Tetratheca pilosa |
| 11 | Sepals present around the mature fruit or tardily caducous, not falling soon after anthesis and with no joint at their junction with the receptacle; stems with usually with gland-tipped hairs | Tetratheca labillardierei |
| Sepals absent from the mature fruit, falling soon after anthesis at a distinct junction with the receptacle; stems hairs not gland-tipped
Back to 4 | 12 |
| 12 | Peduncles and sepals with glandular hairs only | Tetratheca ciliata |
| Peduncles and sepals with non-glandular hairs
Back to 11 | 13 |
| 13 | Sepals usually c. 1 mm long; stem hairs of 2 types, some short and others long | Tetratheca pilosa |
| Sepals more than 1.5 mm long; stem hairs of 1 type only
Back to 12 | 14 |
| 14 | Leaves in whorls | 15 |
| Leaves alternate, rarely opposite
Back to 13 | Tetratheca decora |
| 15 | Most hairs on stems less than 0.5 mm long and curved or curled | Tetratheca bauerifolia |
| Most hairs on stems 0.5–1.5 mm long, tending to be antrorse but many twisted or irregular
Back to 14 | Tetratheca thymifolia |
