The family Acanthaceae (or Acanthus family) is a taxon of dicotyledonous flowering plants containing almost 250 genera and about 2500 species.
Most are tropical herbs, shrubs, or twining vines; some are epiphytes. Only a few species are distributed in temperate regions. The four main centres of distribution are Indonesia and Malaysia, Africa, Brazil and Central America. The representatives of the family can be found in nearly every habitat, including dense or open forests, in scrublands, on wet fields and valleys, at the sea coast and in marine areas, and in swamps and as an element of mangrove woods.
Plants in this family have simple, opposite, decussate leaves with entire (or sometimes toothed, lobed, or spiny) margins, and without stipules. The leaves may contain cystoliths, calcium carbonate concretions, seen as streaks on the surface.
The flowers are perfect, zygomorphic to nearly actinomorphic, and arranged in an inflorescence that is either a spike, raceme, or cyme. Typically there is a colorful bract subtending each flower; in some species the bract is large and showy. The calyx is usually 4-5 lobed; the corolla tubular, 2-lipped or 5-lobed; stamens either 2 or 4 arranged in pairs and inserted on the corolla; and the ovary superior, 2-carpellate, with axile placentation.
The fruit is a two-celled capsule, dehiscing somewhat explosively. In most species, the seeds are attached to a small, hooked stalk (a modified funiculus called a jaculator) that ejects them from the capsule.
A species well-known to temperate gardeners is Bear's Breeches (Acanthus mollis), a herbaceous perennial plant with big leaves and flower spikes up to 2 m tall. Tropical genera familiar to gardeners include Thunbergia and Justicia.
Avicennia, a genus of mangrove tree, usually placed in Verbenaceae or in its own family, Avicenniaceae, is included in Acanthaceae by the Angiosperm Phylogeny Group on the basis of molecular phylogenetic studies that show it to be associated with this family.
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