* Cronquists system of classification (1981)
Urticaceae, or the nettle family, is a family of flowering plants. The family name comes from the genus Urtica (nettles). Urticaceae includes a number of well-known and useful plants, including the aforementioned nettles, Ramie (Boehmeria nivea), māmaki (Pipturus albidus), and ajlai (Debregeasia saeneb).
The family includes approximately 2600 species, grouped into 54 to 79 genera according to the database of the Royal Botanic Gardens, Kew. The largest genera are Pilea (500 to 715 species), Elatostema (300 species), Urtica (80 species), and Cecropia (75 species).
Urticaceae can be found worldwide, apart from the polar regions.
APG II system puts Urticaceae in order Rosales, while older system consider it part of 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.
Urticaceae can be shrubs (e.g. Pilea), lianas, herbs (e.g. Urtica. Parietaria), or, rarely, trees (e.g. Dendrocnide, Cecropia).
Leaves are usually entire and bear stipules. Urticating hairs are often present.
Urticaceae have usually unisexual flowers and can be both monoecious or dioecious. They are pollinated by the wind. Most disperse their pollen when the stamens are mature and their filaments straighten explosively: a peculiar and conspicuously specialised mechanism.
1. ^ Germplasm Resources Information Network (GRIN) (2003-01-17). "Family: Urticaceae Juss., nom. cons.". Taxonomy for Plants. USDA, ARS, National Genetic Resources Program, National Germplasm Resources Laboratory, Beltsville, Maryland. http://www.ars-grin.gov/cgi-bin/npgs/html/family.pl?1165. Retrieved 2008-04-24.
* Stevens, P. F. (2001 onwards). Angiosperm Phylogeny Website. Version 7, May 2006 [and more or less continuously updated since]. 
Source: Wikipedia, Wikispecies: All text is available under the terms of the GNU Free Documentation License