The Urticaceae /ɜːrtɪˈkeɪsiː/ are a family, the nettle family, of flowering plants. The family name comes from the genus Urtica. The Urticaceae include a number of well-known and useful plants, including nettles in the genus Urtica, ramie (Boehmeria nivea), māmaki (Pipturus albidus), and ajlai (Debregeasia saeneb).
The family includes about 2,625 species, grouped into 53 genera according to the database of the Royal Botanic Gardens, Kew and Christenhusz and Byng (2016).[2] The largest genera are Pilea (500 to 715 species), Elatostema (300 species), Urtica (80 species), and Cecropia (75 species). Cecropia contains many myrmecophytes.[3]
Urticaceae species can be shrubs (e.g. Pilea), lianas, herbs (e.g. Urtica, Parietaria), or, rarely, trees (Dendrocnide, Cecropia). Their leaves are usually entire and bear stipules. Urticating (stinging) hairs are often present. They have usually unisexual flowers and can be both monoecious or dioecious. They are wind-pollinated. Most disperse their pollen when the stamens are mature and their filaments straighten explosively, a peculiar and conspicuously specialised mechanism.
The APG II system puts the Urticaceae in the order Rosales, while older systems consider them part of the Urticales, along with Ulmaceae, Moraceae, and Cannabaceae. APG still considers "old" Urticales a monophyletic group, but does not recognise it as an order on its own.
The fossil record of Urticaceae is scattered and mostly based on dispersed fruits. Twelve species based on fossil achenes are known from the Late Cretaceous of Central Europe. Most were assigned to the extant genera Boehmeria (three species), Debregeasia (one species) and Pouzolzia (three species), while three species were assigned to the extinct genus Urticoidea.[4] A Colombian fossil flora of the Maastrichtian stage has yielded leaves that resemble leaves of the tribe Ceropieae.[5] In the Cenozoic fossil leaves from the Ypresian Allenby Formation preserve distinct trichomes, and have been attributed to the Tribe Urticeae in the fossil record. The leaves had originally been identified as Rubus by earlier workers on the Eocene Okanagan Highlands, but Devore et al (2020) interpreted the preserved hairs along the stem and major veins as stinging trichomes, rather than simple hairs or thorns.[6]
Modern molecular phylogenetics suggest the following relationships[7][8] (see also [9][10][11][12][13][14][15][16][17][18]):