Leaves mostly alternate, sometimes 2-ranked, usually simple, rarely reduced to scales; stipules mostly present, often small.
Inflorescence chiefly axillary, sometimes complex but flowers often arranged in bundles or in apparent spikes or racemes or flowers solitary. Flowers actinomorphic, unisexual, sometimes reduced, floral parts hypogynous. Sepals and petals 4–6, sometimes petals absent or perianth not differentiated into sepals and petals. Male flowers with 1–many stamens, anthers 2-locular, dehiscing by longitudinal slits or seldom apical pores; rudimentary ovary sometimes present. Female flowers with superior ovary, usually 3-locular, ovules 1 in each loculus (each locule of ovary with 1 ovule), placentation axile; styles as many as the carpels, free or variously united, often branched; staminodes sometimes present.
Fruit mostly a 3-locular capsule, often schizocarpic, rarely a berry or a drupe; seeds often with a caruncle.
| | Key to the genera | |
| 1 | Either herbs or shrubs (rarely climbers) with either leaves less than 15 mm wide and with entire margins or leaves reduced to scales | 2 |
| Either trees or shrubs (rarely climbers) with either leaves more than 15 mm wide or leaves less than 10 mm wide and the margins toothed | 21 |
| 2 | Inflorescence surrounded by an involucre and containing 1 female flower and 8–10 male flowers; perianth absent | 3 |
| Involucre absent; male and female flowers with perianth
Back to 1 | 4 |
| 3 | Stems erect; leaves usually alternate on lower stems, subopposite or opposite above; stipules minute or absent | Euphorbia |
| Stems prostrate, decumbent or ascending; leaves opposite; stipules present, interpetiolar (former Chamaesyce taxa)
Back to 2 | Euphorbia |
| 4 | Adult stems leafless, scale leaves present on young stems | Amperea |
| Normal leaves developed on all stems
Back to 2 | 5 |
| 5 | Plants with stellate hairs | 6 |
| Plants glabrous or with simple hairs
Back to 4 | 11 |
| 6 | Herbs with ovate to rhombic leaves, usually 20 mm or more wide, petiole at least as long as lamina | 7 |
| Shrubs, or herbs with leaves not as above, 15 mm or less wide; shortly petiolate
Back to 5 | 8 |
| 7 | Plants with a dense, velvety covering of stellate hairs; leaves entire; style 1, simple; capsule smooth | Eremocarpus |
| Plants with a sparse covering of stellate hairs; leaves entire or sinuate-toothed; styles 3, bifid; capsule covered with peltate scales
Back to 6 | Chrozophora |
| 8 | Flowers terminal (sometimes apparently axillary); sepals and petals usually present or rarely petals absent in female flowers | 9 |
| Flowers axillary; perianth usually in 1 whorl or rarely petals reduced or absent
Back to 6 | 10 |
| 9 | Leaves white-woolly with a dense covering of stellate hairs; stipules present | Croton |
| Leaves glabrous, scabrous or with rusty-stellate hairs; stipules absent
Back to 8 | Ricinocarpos |
| 10 | Styles either absent or if present then very short and fused, stigma simple, entire or lobed; fruit 3-seeded | Beyeria |
| Styles 3, obvious, 2–4-branched, stigmas separate; fruit usually 1-seeded
Back to 8 | Bertya |
| 11 | Stipules present, often minute; male flowers with 3–9 stamens | 12 |
| Stipules absent; male flowers with numerous stamens
Back to 5 | 19 |
| 12 | Leaves in groups of 3 at each node, the groups alternate on the stem (see Picrodendraceae) | Micrantheum |
| Leaves not as above, leaves either alternate, opposite or whorled
Back to 11 | 13 |
| 13 | Flowers terminal | 14 |
| Flowers axillary
Back to 12 | 15 |
| 14 | Inflorescence a raceme or corymb, the rachis elongated; anthers opening by terminal pores (see Phyllanthaceae) | Poranthera |
| Inflorescence a dense cyme borne between the 2 terminal leaves at end of stems; anthers opening by longitudinal slits
Back to 13 | Monotaxis |
| 15 | Female flowers enclosed by a large, rounded bract; leaves 20–40 mm long, toothed; petiole at least as long as lamina | Acalypha |
| Female flowers not enclosed by a large bract; leaves to 30 mm long, rarely toothed; petiole shorter than lamina
Back to 13 | 16 |
| 16 | Stamens 6; some leaves opposite, others alternate on the same plant (see Picrodendraceae) | Pseudanthus |
| Stamens 3; leaves all alternate
Back to 15 | 17 |
| 17 | Fruit dry, a schizocarpic capsule; styles bifid | 18 |
| Fruit succulent, a berry; styles unbranched (see Phyllanthaceae)
Back to 16 | Breynia |
| 18 | Disc or glands present; fruit depressed-globose (see Phyllanthaceae) | Phyllanthus |
| Disc or glands absent; fruit ovoid or more or less globose (see Phyllanthaceae)
Back to 17 | Sauropus |
| 19 | Flowers mostly terminal; sepals and petals present, petals conspicuous and longer than the sepals | Ricinocarpos |
| Flowers axillary; perianth in one whorl or the petals rudimentary and shorter than the sepals
Back to 11 | 20 |
| 20 | Styles either absent or if present then very short and fused, stigma simple, entire or lobed; fruit 3-seeded | Beyeria |
| Styles 3, obvious, 2–4-branched, stigmas separate; fruit usually 1-seeded
Back to 19 | Bertya |
| 21 | Leaves with margins toothed, crenate or lobed | 22 |
| Leaves with margins entire or almost so
Back to 1 | 36 |
| 22 | Leaves either unlobed or 3–5-lobed and then the lamina cut less than halfway towards base | 23 |
| Leaves deeply palmately 3–9-lobed, if 3–5-lobed then the lamina cut at least three-quarters of the way towards base
Back to 21 | 35 |
| 23 | Leaves opposite | 24 |
| Leaves alternate
Back to 22 | 25 |
| 24 | Leaves glabrous, finely toothed to crenate (see Picrodendraceae) | Austrobuxus |
| Leaves hairy, coarsely toothed to more or less entire
Back to 23 | Mallotus |
| 25 | Leaves with 1–5 small glands at apex of petiole or near base of lamina | 26 |
| Leaves without glands on lamina or petiole
Back to 23 | 30 |
| 26 | Plants with milky latex; young shoots and leaves glabrous | Excoecaria |
| Plants without milky latex; young shoots and leaves mostly hairy or scaly
Back to 25 | 27 |
| 27 | Leaves palmately 3–5-veined from base, often palmately lobed; petiole about as long as the lamina | 28 |
| Leaves pinnately veined, sometimes 3-veined in basal half; petiole usually shorter than lamina
Back to 26 | 29 |
| 28 | Hairs stellate; ovary 1- or 2-locular; fruit with 1 or 2 seeds | Aleurites |
| Hairs simple; ovary 3–7-locular; fruit mostly with 3–7 seeds
Back to 27 | Vernicia |
| 29 | Petioles with 3–5, rarely 1 or 2, glands on upper surface near apex of petiole; young shoots pubescent, leaves glabrous or sparsely hairy, hairs simple | Claoxylon |
| Petioles with 2 glands at junction with lamina; young shoots and leaves with scales or stellate hairs or sometimes leaves glabrous
Back to 27 | Croton |
| 30 | Climbers; leaves and stems with stinging hairs | Tragia |
| Shrubs or trees; stinging hairs absent
Back to 25 | 31 |
| 31 | Leaves stiff, glabrous; trees or tall shrubs | 32 |
| Leaves soft but firm, glabrous or hairy; shrubs less than 3 m high
Back to 30 | 33 |
| 32 | Teeth spinose, margins with 2–4 pairs of teeth | Alchornea |
| Teeth not spinose, margins with more than 4 pairs of teeth or margins crenate
Back to 31 | Drypetes |
| 33 | Bracts surrounding female flowers and fruits prominent, more or less circular, at least 4 mm and often more than 10 mm diam.; lamina either less than 20 mm long or if more than 20 mm long then pubescent with simple hairs | Acalypha |
| Bracts not as above; lamina more than 20 mm long, mostly stellate-hairy, sometimes glabrous
Back to 31 | 34 |
| 34 | Plants pubescent, sometimes hoary, occasionally glabrous; leaves often lobed; perianth segments 6 or 8, in 2 whorls, c. 6 mm long, not persistent in fruit | Adriana |
| Plants densely tomentose; leaves unlobed; petals absent, calyx 6–9-lobed, persistent in fruit, lobes c. 9 mm long in fruit
Back to 33 | Croton |
| 35 | Margins of leaves toothed, lamina peltate, mostly 7–9-lobed | Ricinus |
| Margins of leaves not toothed, lamina not peltate, mostly 3–7-lobed
Back to 22 | Manihot |
| 36 | Leaves 1-foliolate, with a swelling at apex of petiole and mostly with 2 glands near base of lamina; translucent dots visible in lamina (lens needed); leaves opposite or alternate | 37 |
| Leaves simple, without a swelling at apex of petiole; glands absent or present near base of lamina or apex of petiole; leaves mostly alternate and without translucent dots
Back to 21 | 38 |
| 37 | Buds scaly, reddish brown, more or less glabrous; 2 small embedded glands on margin of lamina c. 3 mm from base; leaves opposite | Baloghia |
| Buds not scaly, finely pubescent with fawn hairs; 2 depressed glands usually on lower lamina surface 5–10 mm from base; adult leaves alternate
Back to 36 | Fontainea |
| 38 | Leaves opposite | 39 |
| Leaves alternate
Back to 36 | 40 |
| 39 | Buds with scale leaves; plants more or less glabrous; leaves with petiole less than 10 mm long, secondary veins more than 10 pairs | Baloghia |
| Buds without scale leaves, plants covered with stellate hairs; leaves with petiole usually more than 10 mm long, secondary veins less than 9 pairs
Back to 38 | Mallotus |
| 40 | Petioles more than 10 mm long; 1 or 2 glands often present near junction of petiole and lamina | 41 |
| Petioles less than 10 mm long, often c. 5 mm long; glands absent or sometimes present in Croton
Back to 38 | 48 |
| 41 | Leaves peltate, petiole attached at least 10 mm in from margin; leaves palmately 9-veined | Macaranga |
| Leaves not peltate or if peltate then petiole attached less than 5 mm in from margin; leaves pinnately veined or palmately 3–5-veined
Back to 40 | 42 |
| 42 | Young shoots and usually young leaves densely covered with hairs and/or scales, hairs simple or stellate | 43 |
| Leaves and shoots glabrous or almost so, hairs if present simple, stellate hairs and scales absent
Back to 41 | 46 |
| 43 | Leaves 3–5-veined from base; scales absent; at least young shoots and leaves hairy, hairs simple or stellate but not woolly | 44 |
| Leaves not 3–5-veined from base; scales present, at least on young shoots, or hairs stellate and plant woolly
Back to 42 | Croton |
| 44 | Lower surface of leaves with scattered, coloured surface glands, usually 3-veined from base; petals absent; leaves not lobed | Mallotus |
| Lower surface of leaves without coloured surface glands, mostly 5-veined from base; petals conspicuous, more than 8 mm long; leaves often lobed
Back to 43 | 45 |
| 45 | Hairs stellate; ovary 1- or 2-locular; fruit 1- or 2-seeded | Aleurites |
| Hairs simple; ovary 3–5-locular; fruit 1–5-seeded
Back to 44 | Vernicia |
| 46 | Leaves more or less triangular, petiole about as long as the lamina; petioles and stems often reddish | Homalanthus |
| Leaves not triangular, petiole less than half as long as the lamina; petioles and stems not reddish
Back to 42 | 47 |
| 47 | Milky latex present; buds without scale leaves; 2 glands present at junction of petiole and lamina | Excoecaria |
| Milky latex absent; buds covered with scale leaves; glands absent from petiole and lamina (see Phyllanthaceae)
Back to 46 | Actephila |
| 48 | Leaves with 12–15 pairs of secondary veins (see Phyllanthaceae) | Bridelia |
| Leaves with less than 12 pairs of secondary veins
Back to 40 | 49 |
| 49 | Young shoots and leaves densely covered with either scales or stellate hairs | Croton |
| Young shoots and leaves glabrous or with simple hairs
Back to 48 | 50 |
| 50 | Leaves distinctly 2-ranked and mostly pseudopinnate in arrangement | 51 |
| Leaves not distinctly 2-ranked, never pseudopinnate in arrangement
Back to 49 | 52 |
| 51 | Lamina less than 30 mm long, glabrous, glaucous below, drying black above; fruit less than 5 mm diam. (see Phyllanthaceae) | Breynia |
| Lamina more than 40 mm long, glabrous or finely pubescent, not glaucous below, not drying black; fruit more than 8 mm diam. (see Phyllanthaceae)
Back to 50 | Glochidion |
| 52 | Leaves glabrous and green on both surfaces, stiff, margin often obscurely crenate; fruit a drupe (see Putranjivaceae) | Drypetes |
| Leaves glabrous and green above on fresh material, sometimes brownish to blackish above when dry, hairy and grey to fawnish below, firm but not stiff, margin entire or almost so; fruit a capsule
Back to 50 | 53 |
| 53 | Leaves grey-green below, sparsely covered with pale-coloured hairs below; green above when dried; capsule 3-lobed, flattened-globose, 5–12 mm diam., green to reddish (see Phyllanthaceae) | Cleistanthus |
| Leaves fawnish grey below, densely covered with fawnish hairs, sometimes more or less glabrescent with age; capsule multilobed, more or less globose, 10–18 mm diam., usually orangey or orange-brown (see Picrodendraceae)
Back to 52 | Petalostigma |
