Herbs, shrubs or trees with abnormal secondary growth. Leaves often opposite or subopposite to alternate, simple. Stipules absent. Flowers cymosely arranged in panicles or corymbs, rarely in umbels or subcapitate, hermaphrodite or unisexual, commonly 5-merous, subtended by a variable number of bractlets which may be small, mostly, or large and conspicuous as in the well-known cultivated genus Bougainvillea, sometimes forming a gamophyllous involucre as in Mirabilis. Perianth single, gamophyllous, often corolla-like, the lower part enclosing the ovary and accrescent with the fruit. Stamens essentially in 1 or 2 whorls, but often irregular in number due to reduction or multiplication; filaments often filiform, more or less united at the base; anthers 2-locular, the thecae reniform or semi-circular. Ovary superior, often stipitate, uni-locular, 1-carpellate; style usually elongate; stigma entire or penicillate. Ovule 1, basal, campylotropous or anatropous. Pericarp very thin, more or less adhering to the testa, the fruit tightly enclosed by the expanded lower part of the perianth which together with the fruit constitutes the anthocarp; anthocarp dry achenium-like or drupe-like, sometimes provided with sticky glands or glandular hairs. Embryo straight or curved; cotyledons frequently unequal. Perisperm present, but often more or less absorbed by the embryo. About 250 species in c. 25 genera, in tropics and subtropics, especially in America.