Leaves opposite, succulent, ± cylindrical to globose or flat and semisucculent, sessile or rarely petiolate.
Flowers 4- or 5-merous. Sepals slightly fused at base. Corolla shortly fused, usually cup-shaped with short spreading lobes. Stamens 4 or 5, hypogynous or perigynous. Carpels free or basally fused, each subtended by a carpel scale, ovary usually gradually tapering into style.
| | Key to the species | |
| 1 | Leaves less than 12 mm long; flowers borne in the axils of leaf-like bracts | 2 |
| Leaves more than 12 mm long; flowers in more or less leafless inflorescences borne well above leaves | 7 |
| 2 | Calyx at least as long as the corolla; flowers in the axils of both leaves at a node; flowers 4- or 5-merous | 3 |
| Calyx half to two-thirds as long as corolla; flowers in the axil of one leaf at each node; flowers 4-merous
Back to 1 | 6 |
| 3 | Flowers mainly 4-merous | 4 |
| Flowers mainly 5-merous
Back to 2 | 5 |
| 4 | Lateral cymes pedunculate | Crassula decumbens |
| Lateral cymes sessile in leaf axils
Back to 3 | Crassula sieberiana |
| 5 | Follicles more or less sessile, pedicels to 1 mm long in fruit | Crassula colorata |
| Follicles distinctly stalked, pedicels to 8 mm long in fruit
Back to 3 | Crassula decumbens |
| 6 | Style less than a quarter as long as ovary, ovary abruptly constricted into the style; leaves 0.5–1 mm wide | Crassula peduncularis |
| Style about half as long as ovary, the ovary gradually tapering into style; leaves 1–2 mm wide
Back to 2 | Crassula helmsii |
| 7 | Leaves more than 10 mm wide, lamina ovate, obovate or broad-elliptic, narrowed into petiole or leaf base | 8 |
| Leaves less than 5 mm wide, linear to triangular, scarcely constricted at base
Back to 1 | Crassula tetragona |
| 8 | Leaves toothed; petiole 0–3 mm long | Crassula sarmentosa |
| Leaves entire; petiole 5–25 mm long
Back to 7 | Crassula multicava |
