1All 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.
4Fruit with rows of distinct spines at the base.
4'Fruit with rows of tubercles at the base.
5Spines present over the entire dorsal length of the mericarps. Madagascar. Fig. 15g.
5'Spines absent in the central part of the mericarps.
6Leaves 2-15 mm long, always opposite. Stamens 8.
6'Leaves 10-30 mm long, mostly alternate. Stamens 4.
7Flowers (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.
8Flowers (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.
9Leaf-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.
10Bracteoles digitate or pinnate.
10'Bracteoles simple, not dissected: ovate, rhomboid, or lanceolate.
11Fruit cruciform in section, finely tubercled, rarely smooth.
11'Fruit in transverse section quadrangular with rounded edges, smooth.
12Stamens 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.
13Fruit 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.
14Flowers (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.
15Flowers (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.
17Mericarps 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.