Leaves alternate, simple, 1-foliolate or palmately compound with 3–7 leaflets; leaflets often with translucent glands; stipulate; stipels absent.
Flowers usually in terminal racemes, sometimes leaf opposed or rarely axillary; bracteate. Calyx 5-toothed, ± equal, sometimes 2-lipped with upper 2 teeth ± united and lower 3 teeth ± united. Corolla venation sometimes dark; standard ± circular or ovate, sometimes pubescent outside; wings shorter than standard, with a patch of ruffles in rows; keel curved to 90?, ciliate, sometimes incurved, beak tip sometimes twisting spirally. Stamen monadelphous, sheath split on upper side; anthers alternately long and basifixed and short and dorsifixed. Ovary ?2-ovuled; style incurved or bent, longitudinal line of hairs on inside; stigma terminal.
Pods inflated, dehiscence sometimes incomplete; seeds ± reniform, with or without an aril, usually smooth, funicles slender.
| | Key to the genus Crotalaria | |
| 1 | Leaves simple or 1-foliolate. | 2 |
| 2 | Leaves 2-10 mm wide, mostly linear to oblong, occasionally elliptic. | 3 |
| 3 | Ovary and pods hairy; pods 2.5-3.5 cm long; leaves usually 4-6.5 cm long. | Crotalaria juncea |
| 3* | Ovary and pods glabrous; pods 0.6-1 cm long; leaves mostly 0.4-4 cm long. | 4 |
| 4 | Erect plants to 1 m high; leaves 2-5 cm long, length:breadth ratio of 5-20:1; inflorescences with usually 7-35 well-separated flowers on racemes to 30 cm long; standard petal circular, emarginate at apex. | Crotalaria montana |
| 4* | Ascending or erect plant with many stems, to 40 cm high; leaves usually 0.6-2.5 cm long, with length:breadth ratio of 2-8:1; inflorescences with up to 10 flowers, usually crowded or overlapping on racemes less than 10 cm long; standard petal ovate to oblong or obovate, acute or rounded at apex. | Crotalaria brevis |
| 2* | Leaves >10 mm wide, ovate to obovate or elliptic to lanceolate. | 5 |
| 5 | Stipules leafy, broad-ovate to broad-falcate, to 10 mm long, persistent. | 6 |
| 6 | Shrub or small tree 2-5 m high; stems and lower surface of leaves densely pubescent, sometimes glabrescent; calyx hairy. | Crotalaria lunata |
| 6* | Shrub to 2 m high; stems and lower surface of leaves glabrous, ± glaucous; calyx glabrous. | Crotalaria spectabilis |
| 5* | Stipules linear to narrow-ovate, to 5 mm long, sometimes caducous. | 7 |
| 7 | Leaves simple, upper surface glabrous. | Crotalaria mitchellii |
| 7* | Leaves 1-foliolate, upper surface of leaves densely tomentose, although sometimes glabrescent. | 8 |
| 8 | Leaves 1-4 cm long; flowers c. 8 mm long, mostly yellow and red; plants prostrate to ascending, <50 cm high. | Crotalaria smithiana |
| 8* | Leaves 4-7 cm long; flowers mostly 40-45 mm long; greenish yellow; plants erect to 1 m high. | Crotalaria cunninghamii |
| 1* | Leaves 3-7-foliolate. | 9 |
| 9 | Leaflets 5-7. | Crotalaria grahamiana |
| 9* | Leaflets 3. | 10 |
| 10 | Stipules leafy, to 25 mm long. | Crotalaria goreensis |
| 10* | Stipules not as above. | 11 |
| 11 | Ovary and pods glabrous; flowers 20-55 mm long. | Crotalaria agatiflora |
| 11* | Ovary and pods ± pubescent; flowers <20 mm long. | 12 |
| 12 | At least terminal leaflets mostly >3 cm long. | 13 |
| 13 | Leaflets broad-obovate to broad-elliptic, to 4.5 cm wide. | 14 |
| 14 | Racemes c. 10-flowered; stipules ± filiform, 2-15 mm long, persistent; stem hairs short and curved-ascending or long and spreading. | Crotalaria incana |
| 14* | Racemes c. 40-flowered; stipules absent or rarely to 3 mm long and then caducous; stem hairs short and appressed. | Crotalaria pallida |
| 13* | Leaflets linear or oblong to lanceolate or elliptic, occasionally obovate, to 2.5 cm wide. | 15 |
| 15 | Lateral leaflets much reduced, usually less than half the length of terminal leaflet; stems and leaves mostly grey-pubescent. | Crotalaria eremaea |
| 15* | Lateral leaflets usually at least half the length of the terminal leaflet; stems and leaves not grey-pubescent. | 16 |
| 16 | Calyx tube pubescent; leaflets mostly <1 cm wide; pods 2-3.5 cm long. | 17 |
| 17 | Stipules linear, 1-3 mm long, ± persistent; upper or both surfaces of leaflets glandular; flowers yellow, without markings. | Crotalaria dissitiflora |
| 17* | Stipules absent or minute; upper surface of leaflets not glandular; flowers yellow with purplish brown markings. | Crotalaria lanceolata |
| 16* | Calyx tube glabrous; leaflets 0.8-2.5 cm wide; pods 3.5-4.5 cm long. | Crotalaria zanzibarica |
| 12* | Leaflets mostly <3 cm long. | 18 |
| 18 | Leaflets >1 cm wide. | Crotalaria incana |
| 18* | Leaflets mostly <1 cm wide. | 19 |
| 19 | Pods 2-seeded, c. 5 mm long. | Crotalaria medicaginea |
| 19* | Pods >2-seeded, >10 mm long. | 20 |
| 20 | Leaflets hairy on both surfaces; lateral leaflets much reduced, usually less than half the length of terminal leaflet. | Crotalaria eremaea |
| 20* | Leaflets glabrous above; lateral leaflets usually at least half the length of terminal leaflet. | 21 |
| 21 | Flowers c. 30 per raceme; upper surface of leaflets glandular. | Crotalaria dissitiflora |
| 21* | Flowers 1-10 per raceme; upper surface of leaflets not glandular. | 22 |
| 22 | Racemes of 1-8 flowers in axils of upper leaves; leaflets obovate to narrow-obovate, terminal leaflet 7-15 mm long. | Crotalaria virgulata |
| 22* | Racemes of 8-16 flowers, terminal and leaf-opposed; leaflets narrow-elliptic to oblanceolate, terminal leaflet 10-30 mm long. | Crotalaria distans |
