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Description


Monoecious or dioecious herbs, shrubs, or trees. Stems fibrous, sometimes armed with stinging hairs. Leaves simple, alternate or opposite, petiolate. Inflorescences axillary, cymose, paniculate raceme, spicate, or cluster-capitate, usually formed from glomerules, sometimes crowded on common receptacle, rarely solitary. Flowers minute, unisexual or bisexual, actinomorphic, 4- or 5-merous, rarely perianth absent in female flowers. Perianth 1-whorled. Male flowers: stamens usually 3-5, opposite to tepals, or reduced to 2 or 1, anthers 2-celled, rudimentary pistillode present. Female flowers: perianth lobes free or connate, usually enlarged in fruit and persistent; staminodes scarious, opposite to the perianth lobes, or absent; ovary superior, sessile or shortly stipitate, unilocular, with one basal ovule, style 1 or absent, simple, stigmas diverse, capitate, mostly penicillate, subulate, filiform, ligulate, or peltate. Fruits achenes, nuts, or fleshy drupes, often enclosed by persistent perianths. Seeds solitary with membranous testa.

Key to the Genus

Serial Key Reference
1a. Plants armed with stinging hairs; female flowers without staminodes 2
1b. Plants without stinging hairs; female flowers with or without staminodes 5
2a. Leaves opposite; perianth lobes of female flowers free Urtica
2b. Leaves alternate; perianth lobes of female flowers connate 3
3a. 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 Girardinia
3b. Female perianth lobes 4, dorsal lobe largest, ventral lobe smallest, joined at base only, never bristlelike; ± woody shrub or tree or herbs with longest stinging hairs less than 5 mm 4
4a. Stipules completely joined, apex entire; trees or shrubs; pedicels of female flowers absent terete, not winged in fruit Dendrocnide
4b. Stipules 2-fid at apex; herbs or subshrubs; pedicels of female flowers always present, winged in fruit Laportea
5a. Cystoliths usually linear or fusiform; stigma sessile, penicillate-capitate; perianth lobes of female flowers free or connate at base, staminodes present 6
5b. 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 8
6a. Leaves opposite, rarely spirally alternate and then leaf blade peltate; leaf blade usually symmetric Pilea
6b. 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 7
7a. 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 Elatostema
7b. 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 Pellionia
8a. Leaves opposite 9
8b. Leaves alternate 13
9a. Leaf blade margin entire 10
9b. Leaf blade margin serrate or dentate 11
10a. Male buds truncate, perianth with annular, often villous, crown formed from transverse crests of lobes; leaf blade 3-veined from base Gonostegia
10b. Male flowers without this combination of characters; leaf blade with at least 2 major lateral veins arising clearly above base Pouzolzia
11a. Perianth membranceous and enclosing the achene 12
11b. Fruiting perianth absent Phenax
12a. Achene not lustrous, remaining attached to perianth; stigma persistent Boehmeria
12b. Achene lustrous, easily detached from perianth; stigma usually deciduous Pouzolzia
13a. Stigma filiform or ligulate 14
13b. Stigma penicillate, peltate or ringlike 16
14a. Slender herb with small bisexual flower-clusters arranged along slender leafless unbranched spike-like axes. Staminate flowers 2-merous Neodistemon
14b. Herb or shrub with flower-clusters variously axillary or along branched or unbranched axes (Fig. 3) but staminate flowers 3–5-merous 15
15a. Male buds truncate, perianth with annular, often villous, crown formed from transverse crests of lobes; leaf blade 3-veined from base Gonostegia
15b. Male flowers without this combination of characters; leaf blade with at least 2 major lateral veins arising clearly above base Pouzolzia
16a. Inflorescence elongated with short lateral branches, all axes completely hidden by very closely spaced flowers; stigma ringlike Sarcochlamys
16b. Inflorescence globose or nearly so or, if more elongated and branched then axes exposed between discrete glomerules of flowers; stigma peltate or penicillate 17
17a. 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 Oreocnide
17b. Stigma penicillate; achene without fleshy receptacle Debregeasia