Cactaceae belong almost entirely to the New World; but some of the Opuntias have been so long distributed over certain parts of Europe, especially on the shores of the Mediterranean and the volcanic soil of Italy, that they appear in some places to have taken possession of the soil, and to be distinguished with difficulty from the aboriginal vegetation.
The similarity of certain xerophilous Euphorbiaceae to Cactaceae is a ready illustration of this phenomenon.
The western dry areas have the old-world leguminous Astragalus and Prosopis (Mesquit), but are especially characterized by the northward extension of the new-world tropical Cactaceae, Mgmmillaria, Cereus and Opuntia, by succulent Amar llideae such as A gave (of which the so-called American aloe is a type), and by arborescent Liliaceae (Yucca).
Cactaceae are widely spread and both northwards and southwards extend into temperate regions.
The nearly related Ficoideae replace the new-world Cactaceae, but the habit of the latter is simulated by fleshy Euphorbias and Asclepiads, just as that of A gave is by the liliaceous Aloe.
