Agavaceae is a family of plants that includes many well-known desert and dry zone types such as the agave, yucca, and Joshua tree. The family includes about 550-600 species in around 18 genera, and is widespread in the tropical, subtropical and warm temperate regions of the world.
The circumscription of this family has varied widely. Some genera (e.g. Cordyline and Dracaena) are sometimes separated off into a separate family, Dracaenaceae, though recent research has tended to incorporate these into a larger family Ruscaceae. Nolina, Beaucarnea, and Dasylirion are sometimes recognized as Nolinaceae or placed in Ruscaceae. Conversely, data from molecular systematics now suggest that Agavaceae should be broadened to include a number of genera previously classified elsewhere, among them Chlorogalum, Camassia and the family Anthericaceae with anything up to 22 additional genera. The Angiosperm Phylogeny Group's APG II classification places Agavaceae, along with a number of other families (including Ruscaceae) in an expanded family Asparagaceae. However, APG II allows the alternative of keeping some of these families, including Agavaceae, separate, though in this case it recommends expanding the family to include the genera currently classified in Anemarrhenaceae, Anthericaceae (with Anthericum and Paradisea), Behniaceae and Herreriaceae. Most references have retained Agavaceae (in varying circumscriptions) as a family distinct from Asparagaceae. Hesperocallis, sometimes placed in its own family, Hesperocallideaceae, has recently been shown to be closely related and its inclusion in Agavaceae has been recommended (Pires et al. 2004).
Species may be succulent or not. In general, Agavaceae leaves occur as rosettes at the end of a woody stem, which may range from extremely short to tree-like heights, as in the Joshua tree. The leaves are parallel-veined, and usually appear long and pointed, often with a hardened spine on the end, and sometimes with additional spines along the margins.