1	Filaments of stamens erect in bud; shrubs or woody climbers.		18 Poikilospermum
+	Filaments of stamens inflexed in bud; usually not woody climbers.		(2)
2 (1)	Plants armed with stinging hairs; female flowers without staminodes.		(3)
+	Plants without stinging hairs; female flowers with or without staminodes.		(7)
3 (2)	Leaves opposite; perianth lobes of female flowers free, lateral pair outer and much smaller than dorsiventral pair.		1 Urtica
+	Leaves alternate; perianth lobes of female flowers connate or if free then not as above.		(4)
4 (3)	Stipules interpetiolar; achene straight, sessile; stigma penicillate-capitate; slender herb to 40 cm.		2 Nanocnide
+	Stipules intrapetiolar; achene strongly oblique, stipitate; stigma filiform, ligulate, or subulate; trees, shrubs or usually robust herbs.		(5)
5 (4)	Female perianth with 3 lobes fused and the 4th absent or reduced to a bristle; robust herb with longest stinging hairs more than 5 mm.		5 Girardinia
+	Female perianth lobes 4, dorsal lobe largest, ventral lobe smallest, joined at base only, never bristle-like; ± woody shrub or tree or herbs with longest stinging hairs less than 5 mm.		(6)
6 (5)	Stipules completely joined, apex entire; trees or shrubs; pedicels of female flowers absent or terete, not winged in fruit.		4 Dendrocnide
+	Stipules 2-fid at apex; herbs or subshrubs; pedicels of female flowers always present, winged in fruit.		3 Laportea
7 (2)	Cystoliths usually linear or fusiform; stigma sessile, penicillate-capitate; perianth lobes of female flowers free or connate at base, staminodes present (except in Procris).		(8)
+	Cystoliths dotlike or very short blunt rods (botuliform); stigma often on a style, mostly linear, less often penicillate-capitate; perianth lobes of female flowers usually connate into a tube, rarely strongly reduced, or absent, staminodes absent.		(12)
8 (7)	Leaves opposite, rarely spirally alternate and then leaf blade peltate; leaf blade usually symmetric.		(9)
+	Leaves alternate or very strongly heterophyllous with 1 leaf of the pair reduced to a nanophyll very much smaller than the other, leaves usually distichous; leaf blade usually asymmetric.		(10)
9 (8)	Flowers usually forming loose cymes or cymose panicles, sometimes spikes or in clusters; achene without crested appendix at apex.		6 Pilea
+	Flowers inserted on discoid or concave, fleshy receptacle; achene with crested or U-shaped appendix at apex.		7 Lecanthus
10 (8)	Perianth lobes of female flowers usually 4 or 5, much shorter than ovary, or strongly reduced, not corniculate at apex; achene 6-10-ribbed; male inflorescences usually with receptacle, rarely cymose; female inflorescences with discoid receptacle and bracteoles along margin.		9 Elatostema
+	Perianth lobes of female flowers 3-5, longer than ovary, usually corniculate below apex; achene tuberculate or striate, rarely smooth, never ribbed; male inflorescences cymose; female inflorescences cymose or captitate on globose receptacle.		(11)
11 (10)	Female inflorescences cymose, rarely with discoid receptacle and involucre; perianth lobes of female flowers (4 or)5; staminodes present.		8 Pellionia
+	Female inflorescences capitate on globose receptacle, but without involucre; perianth lobes of female flowers 3 or 4; staminodes absent.		10 Procris
12 (7)	Stipules absent; flowers sometimes bisexual, each subtended by 1 or more leaflike bracts longer than the flower, contrasting with the chaffy brown perianth and glossy black achene.		24 Parietaria
+	Stipules present; flowers unisexual, bracts and flowers not as above.		(13)
13 (12)	Inflorescence enclosed within involucre, usually bisexual with several male flowers surrounding 1 or 2 female flowers; male flower with 1 stamen; female flower without perianth.		25 Droguetia
+	Inflorescence without involucre, often unisexual; male flower with 3-5 stamens; female flower with tubular perianth around ovary.		(14)
14 (13)	Leaves opposite.		(15)
+	Leaves alternate.		(20)
15 (14)	Leaf blade margin entire.		(16)
+	Leaf blade margin serrate or dentate.		(17)
16 (15)	Male buds truncate, perianth with annular, often villous, crown formed from transverse crests of lobes; leaf blade 3-veined from base.		15 Gonostegia
+	Male flowers without this combination of characters; leaf blade with at least 2 major lateral veins arising clearly above base.		14 Pouzolzia
17 (15)	Stigma ovoid-capitate, on short style; stipules persistent, reflexed at flowering; slender stoloniferous herb.		13 Chamabainia
+	Stigma elongated; stipules often deciduous; shrub or herb, not stoloniferous.		(18)
18 (17)	Stigma minute, less than 0.5 mm, hooked, persistent; fruit symmetrically enlarged at apex; inflorescences paired at nodes, sessile, ± globose, very dense with base partly enveloping stem.		16 Cypholophus
+	Stigma relatively long, variously curved [but if hooked then more than 1 mm], sometimes deciduous; fruit ± symmetric at apex, often winged; inflorescence various, often pedunculate, if sessile then base not enveloping stem.		(19)
19 (18)	Achene not lustrous, remaining attached to perianth; stigma persistent.		12 Boehmeria
+	Achene lustrous, easily detached from perianth; stigma usually deciduous.		14 Pouzolzia
20 (14)	Stigma filiform or ligulate.		(21)
+	Stigma penicillate, peltate or ringlike.		(24)
21 (20)	Stigma ligulate.		11 Archiboehmeria
+	Stigma filiform.		(22)
22 (21)	Female perianth fleshy at maturity, apex with tiny, entire opening, lobes completely fused; style deciduous.		19 Pipturus
+	Female perianth not fleshy, apex minutely 2-toothed; style often persistent.		(23)
23 (22)	Achene not lustrous, remaining attached to perianth; stigma persistent.		12 Boehmeria
+	Achene lustrous, easily detached from perianth; stigma usually deciduous.		14 Pouzolzia
24 (20)	Inflorescence elongated with short lateral branches, all axes completely hidden by very closely spaced flowers; stigma ringlike.		17 Sarcochlamys
+	Inflorescence globose or nearly so or, if more elongated and branched then axes exposed between discrete glomerules of flowers; stigma peltate or penicillate.		(25)
25 (24)	Stigma peltate with long ciliate hairs along margin; achene adnate to thinly fleshy perianth, surrounded at base or almost wholly enclosed by discoid or cuplike fleshy receptacle.		20 Oreocnide
+	Stigma penicillate; achene without fleshy receptacle.		(26)
26 (25)	Perianth of female flowers inconspicuous, connate into a shallow pocket or absent; leaves usually discolorous, abaxially white tomentose.		23 Maoutia
+	Perianth of female flowers conspicuous, connate into a tube; leaves sometimes concolorous.		(27)
27 (26)	Female perianth small, cupular, 4 or 5-lobed or -toothed, adnate to base of ovary; inflorescences paired, unbranched pedunculate heads.		22 Leucosyke
+	Female perianth enclosing ovary, tube obovoid or jug-shaped, mouth contracted, very minutely 3- or 4-toothed, in fruit often enlarged, fleshy, and adnate to ovary, rarely membranous and free; inflorescences often branched.		21 Debregeasia