An order of flowering plants (Magnoliophyta, or angiosperms), in the subclass Asteridae (Eudicotyledons). The order consists of some 22 families with approximately 1100 genera and over 21,000 species. Seven families (Acanthaceae, Gesneriaceae, Lamiaceae, Orobanchaceae, Plantaginaceae, Scrophulariaceae, Verbenaceae) have more than 1000 species. Members of the Lamiales are distributed worldwide with some families being predominantly tropical and some being predominantly temperate. Lamiaceae, the largest family, is well represented in both tropical and temperate floras.
A basal split in the evolutionary relationships within the order sets off the family Oleaceae, with tetramerous flowers, which are radially symmetric, from the rest of the Lamiales. Pentamerous flowers with fewer stamens (two or four) than petals and bilateral symmetry predominate among the other families. Flowers of all families are characterized by petals fused into a tubular corolla, a single whorl of stamens (typically four), and ovaries consisting of two fused carpels. Iridoid compounds are found in most members of the Lamiales and are thought to function in deterring herbivory by insects. However, iridoids are not universal in the order and, for example, the large subfamily Nepetoideae in family Lamiaceae lacks iridoids but exhibits a diverse array of volatile oils that may serve a similar function.
The volatile oils in the Lamiaceae have made many species valuable as scents and herbs, including lavender (Lavandula), mint (Mentha), sage (Salvia), catnip (Nepeta), basil (Ocimum), and oregano (Oreganum). Additional economically important plants in the Lamiales include those grown for food: sesame (Sesamum, Pedaliaceae) and olives (Olea, Oleaceae); wood: teak (Tectona, Verbenaceae) and ash (Fraxinus, Oleaceae); houseplants: African violets and relatives (Gesneriaceae); and many ornamental plants from a wide variety of families. The order also contains some plants with specialized habits, including parasitic plants (Orobanchaceae), insectivorous plants (Byblidaceae, Lentibulariaceae), mangroves (Avicenniaceae), and aquatic plants, such as Callitriche and Hippuris (Plantaginaceae). See also Asteridae; Magnoliophyta; Magnoliopsida; Plant kingdom.