| 1 | All leaves alternate to opposite, entire or dentate, or the lower ones pinnate. |
| 1' | At least the lower leaves in whorls, nearly always pinnate. |
| 2 | ♂ Flower with 2 petals and 1 stamen. Bracteoles minute or 0. |
| 2' | ♂ Flower with 4 petals and 4 or 8 stamens. Bracteoles small but conspicuous, at least those of the ♂ flowers. |
| 3 | ♂ Flower stalked. Fruit with 4 mericaps. North Vietnam. Fig. 15d-f. |
| 3' | ♂ Flower sessile. Fruit with 2 mericarps. |
| 4 | Fruit with rows of distinct spines at the base. |
| 4' | Fruit with rows of tubercles at the base. |
| 5 | Spines present over the entire dorsal length of the mericarps. Madagascar. Fig. 15g. |
| 5' | Spines absent in the central part of the mericarps. |
| 6 | Leaves 2-15 mm long, always opposite. Stamens 8. |
| 6' | Leaves 10-30 mm long, mostly alternate. Stamens 4. |
| 7 | Flowers (1-)2(-3) on each branchlet, strictly monoecious, on each branchlet of one sex. Stems upwardly very much sympodially branched, with very short internodes 0.3-1 mm long. Leaves caducous. Sepals in ♂ flowers 0. |
| 7' | More flowers on each branchlet, the upper ♂ the lower ♀, or plant dioecious. Stems with much longer internodes, monopodially branched. Leaves not caducous. Sepals in ♂ flower very conspicuous. |
| 8 | Flowers (1-)3-5 together, distinctly stalked. Fruit c. 1¼ by 1 mm, with dorsally rounded mericarps. S. India. Fig. 14q-t. |
| 8' | Flowers solitary, sessile or nearly so. Fruit c. 2½ by 2 mm, in transverse section ± quadrangular with sharp ribs and slightly concave sides. |
| 9 | Leaf-base ± dilated, those of a whorl, at least in sterile branches, enclosing the stem at the nodes in the upper parts. Bracteoles subulate, sometimes with 1 or 2 lateral laciniae. |
| 9' | Stem always visible on the nodes between the leaf-bases. Bracteoles either not subulate, or with more laciniae. |
| 10 | Bracteoles digitate or pinnate. |
| 10' | Bracteoles simple, not dissected: ovate, rhomboid, or lanceolate. |
| 11 | Fruit cruciform in section, finely tubercled, rarely smooth. |
| 11' | Fruit in transverse section quadrangular with rounded edges, smooth. |
| 12 | Stamens 8. Anther linear, 1½-1¾ mm. Petals 1½-2 mm. Ceylon, S. India. Fig. 14d-g. |
| 12' | Stamens 4. Anthers oblong, 0.6-0.8 mm. Petals c.1(-1½)mm long. |
| 13 | Fruit with 2(-4) mericarps, smooth or indistinctly lengthwise lineolate, stalked. |
| 13' | Fruit with 4 mericarps of which sometimes 1-2 are visible but reduced and unfertile, not lineolate. |
| 14 | Flowers (1-)2-6 together in the leaf-axil; the middle flower ☿, shortly but distinctly stalked. |
| 14' | Flowers always solitary, either all sessile, or the ♂ flowers stalked. |
| 15 | Flowers (1-)3-5(-6) together in the leaf-axil. Fruit rounded, shallowly 4-sulcate, tuberculate. Anthers c. 1 mm long. S. India. Fig. 14q-t. |
| 15' | Flowers 1-3 together. Fruit ± cruciform, dorsally narrowly winged, smooth or punctate. Anthers c. 2 mm long. Madagascar. Fig. 16. |
| 16 | ♂ Flower distinctly stalked. Stamens inserted on a 0.1-0.2 mm high androphore. Mericarps apically spreading by the cushion-like thickened style-bases. |
| 16' | All flowers sessile. Androphore 0. Mericarps not spreading at apex. |
| 17 | Mericarps dorsally rounded. Sepals in ♂ flowers distinct, c.½ by ½ mm. Stamens 8. Petals caducous. |
| 17' | Mericarps dorsally acute. Sepals indistinct. Stamens 4. Petals strongly recurved after anthesis, persistent until fruit is set. |
