but much modified. Further testing of the key required.
| 1 | Shrub; 1-3 m high |
| 1' | Annual or perennial herb; much less than 1 m high |
| 2 | Pods produced underground (geocarpic) |
| 2' | Pods produced above ground |
| 3 | Pods stellate-spreading in axillary clusters; sessile or very shortly pedunculate; pods straight or slightly curved |
| 3' | Pods not stellate-spreading; distinctly pedunculate, sometimes shortly pedunculate (less than 2 mm) but then pods coiled into a close spiral |
| 4 | Flowers 8-10 mm long; pod almost straight, or falcate, or forming an open spiral; plants perennial; leaflets glabrous or thinly pilose |
| 4' | Flowers 2-8 mm long; pod reniform or coiled into a close spiral; petals yellow |
| 5 | Pod coiled 1.5-3.5 times; flowers violet or purple |
| 5' | Pod falcate-circinnate, or coiled 1-1.5 times; flowers yellow, violet, purple, greenish or whitish |
| 6 | Pods reniform, blackish when ripe, 1-seeded; flowers in dense globose or oblong-cylindrical clusters |
| 6' | Pods spirally coiled, at least some with 2 or more seeds |
| 7 | Leaves and stems densely villose; inflorescences capitate-racemose, conspicuous; perennial plant of sandy seashores and sand-dunes |
| 7' | Leaves and stems not densely villose; plants annual |
| 8 | Pod without spines, flat, discoid, 12-16 mm diam.; seeds with a tuberculate-rugulose testa |
| 8' | Pod not as above; seeds with a smooth testa |
| 9 | Some pod coils conspicuously imbricate (as in a stack of bowls) |
| 9' | Pod coils more or less flat (as in a stack of coils) |
| 10 | Open part of 'bowls' all point towards distal end |
| 10' | Open part of 'bowls' point towards middle |
| 11 | Pod without spines |
| 11' | Pod with small spines |
| 12 | Pod without spines |
| 12' | Pod spinose (spines sometimes short and blunt) |
| 13 | Stems and leaves glandular |
| 13' | Stems and leaves not glandular |
| 14 | Peduncle long and slender, usually exceeding subtending leaf; inflorescence usually 3-8-flowered |
| 14' | Peduncle rather short, not exceeding subtending leaf; inflorescence 1-3-flowered |
| 15 | Dorsal surface of pods, and spines, +/- densely clothed with short multicellular hairs |
| 15' | Dorsal surface of pods, and spines, glabrous or thinly clothed with simple hairs |
| 16 | Spines short, thick, erect; pods 5-8(-12) mm diam. |
| 16' | Spines long, slender, spreading; pods 9-15(-17) mm diam. |
| 17 | Fruiting peduncles long and slender, usually equalling or exceeding the subtending leaves |
| 17' | Fruiting peduncles generally shorter than subtending leaves |
| 18 | Pods less then 5 mm diam.; leaves and stems distinctly pilose; inflorescences capitate |
| 18' | Pods more than 5 mm diam. |
| 19 | Spines spreading at a right angle to lateral surfaces of pod; leaflets narrowly obovate or elliptic, sometimes lobed or lacinate |
| 19' | Spines erect; leaflets broadly obovate, obcuneate or obcordate, not lobed or laciniate |
| 20 | Pods discoid or very shortly cylindrical, spines often long and reflexed; distal coils of pod often unarmed |
| 20' | Pods subglobose ovoid or barrel-shaped, spines usually short and thick |
| 21 | Inflorescence usually 1-2-flowered; standard about 4 mm long; pod subglobose or broadly ovoid; small prostrate plant, stems usually less than 15 cm long |
| 21' | Inflorescence usually 3-8-flowered; standard about 6 mm long; pod usually barrel-shaped; rather robust plant, stems 15-50 cm long |
| 22 | Leaflets glabrous above, subglabrous or thinly pilose below |
| 22' | Leaflets more or less pilose or pubescent on both surfaces |
| 23 | Inflorescence 1-2(-3)-flowered (several plants to be checked) |
| 23' | Inflorescence 2-8(-10)-flowered (several plants to be checked) |
| 24 | Leaflets 2-6 mm long; pod with up to 4(-5) coils, c. 2.5-4.5 mm wide; seeds c. 2.5 mm long; spines relatively thin and flexible |
| 24' | Leaflets 7-15 mm long; pod with 5-9 coils, 4-10 mm wide; seeds 3-5 mm long; spines stocky and difficult to bend |
| 25 | Pod edge shows fewer than 4 ridges; lateral surfaces of pods distinctly reticulate-veined; pod usually with erect spines; leaflets without blotches; stipules laciniate with slender fliform teeth; stems glabrous or subglabrous |
| 25' | Pod edge shows 4 ridges alternating with 3 groves; lateral surfaces of pods obscurely veined; pod with spreading spines; leaflets usually blotched; stipules deeply dentate or shortly laciniate with narrowly deltoid teeth; stems normally clothed with scattered multicellular hairs |
| 26 | Stipules entire or subentire; inflorescence usually 3-6-flowered; pods with slender spines |
| 26' | Stipules dentate-laciniate; inflorescence 1-3-flowered; pods with rather short, thick spines |
| 27 | Dorsal surface of pod glabrous with erect or suberect spines; dorsal suture not distinctly raised |
| 27' | Dorsal surface of pod more or less pilose with spreading spines; dorsal suture raised with a furrow on either side |
