This new key needs further testing.
| 1 | Leaves hastate or sagittate |
| 1' | Leaves not hastate or sagittate |
| 2 | Inner perianth segments not accrescent in fruit, not or little larger than the nut |
| 2' | Inner perianth segments accrescent in fruit, larger than the nut |
| 3 | Margins of fruiting valves spinulose or rarely subentire, with marginal vein; valves distinctly unequal |
| 3' | Margins of fruiting valves entire, without marginal vein; valves subequal |
| 4 | Valves entire, sometimes denticulate, but without conspicuous teeth |
| 4' | Valves conspicuously dentate, with teeth at least 0.5 mm long |
| 5 | Tubercles occupying the greater part of the surface of the valve; panicles with rather long divaricate branches; leaves more or less flat |
| 5' | Tubercles inconspicuous, occupying less than one third of the width of the valve; leaves conspicuously crisp-undulate |
| 6 | Plants annual, to about 30 cm high (usually much smaller); valves 2-4 mm long; fruiting pedicel often flattened or dilated |
| 6' | Plants up to 150 cm high, annual or perennial, if less than 30 cm, then perennial; valves 3-8 mm long; fruiting pedicel terete |
| 7 | Valves broadly triangular, leathery, with 2(-3) stout, broadly-based teeth on each margin |
| 7' | Valves lingulate and entire, or narrowly triangular with (2-)3-4 slender teeth on each margin |
| 8 | Valves clearly dentate in fruit, the teeth at least 1 mm long |
| 8' | Valves entire or denticulate in fruit, the teeth rarely as much as 1 mm long |
| 9 | Annual; inflorescence simple and spiciform, or with lax, erect or ascending branches; valves 3-4 mm wide |
| 9' | Perennial; inflorescence a lax panicle, with long, spreading branches; valves 4-7 mm wide -- go to key point 11 |
| 10 | Branching not strongly divaricate, becoming rather crowded; pedicels thin, longer than perianth segments; margins of fruiting valves irregularly erose-denticulate; largest callus 2-3 x 1.5 mm |
| 10' | Branching strongly divaricate; pedicels thick, about as long as perianth segments; margins of fruiting valves pectinate-spinulose, occasionally subentire; largest callus c. 2 x 1 mm |
| 11 | Valves entire, or with a few teeth not more than 0.5 mm long near the base |
| 11' | Valves with several teeth on each margin; teeth more than 0.5 mm long |
| 12 | Valves broadly deltoid or suborbicular, 6-7 x 6-7 mm; teeth short, up to 8 on each margin |
| 12' | Valves narrowly ovate, oblong or oblong-deltoid with lingulate apex, less than 6 mm wide; 4-6 teeth on each margin |
| 13 | Valves c. 6 mm long; teeth 3-4 mm long, 5-6 on each margin |
| 13' | Valves 4-6 mm long; teeth 1-2 mm long, sometimes longer, 4 on each margin |
| 14 | Inflorescence much branched; valves 4-5 mm long; teeth 1-2 mm long; basal leaves usually panduriform |
| 14' | Inflorescence unbranched or with few, elongate branches; valves 4-6 mm long; teeth 1-2 mm long or longer; leaves not panduriform |
