General description:- Herbs, small shrubs or rarely climbers, without latex.
Leaves:- Opposite or alternate, simple, usually stipulate.
Flowers:- Usually unisexual. Perianth 4- or 5-merous, often persistent. Male flowers with (1-)4 or 5 stamens opposite the perianth-segments and inflexed in bud, often with rudimentary ovary. Female flowers often with small staminodes; ovary superior, 1-locular, sometimes adnate to perianth; style simple; ovule 1, orthotropous.
Fruit:- An achene. Seeds usually with endosperm.
PARIETARIA
General description:- Annual or perennial herbs, sometimes woody at the base, without stinging hairs.
Leaves:- Alternate, entire; stipules absent.
Flowers:- Hermaphrodite or unisexual, in axillary, bracteate, 3- to many-flowered cymes, 1 or more in each leaf-axil. Perianth green, cylindrical and 4-toothed in female flowers, 4-partite in hermaphrodite and male flowers.
Fruit:- Achenes enclosed in the perianth and sometimes in the bracts.
Key features:-
1) Flowers clustered.
2) Stems not creeping or rooting at the nodes.
URTICA
General description:- Annual or perennial herbs, with stinging hairs.
Leaves:- Opposite, usually variously toothed or deeply lobed; stipules 4, free or connate in pairs.
Flowers:- Inflorescence axillary, spike-like, with clustered ultimate branches. Flowers unisexual, plants monoecious or dioecious. Perianth 4-merous. Female flowers with more or less unequal perianth-segments, the 2 larger enclosing the achene.
Key features:-
1) Leaves 10 mm or more, green beneath, opposite, variously toothed or lobed, rarely entire and with stinging hairs.
2) Female flowers with perianth enclosing the achene, male flowers with 4 stamens and deeply lobed perianth