LAMIALES

the mint order of the flowering plants, belonging to the class called dicotyledon (Magnoliopsida; characterized by two seed leaves). It comprises some 7,800 species in four families. The mint (Lamiaceae) and the verbena (Verbenaceae) families account for some three-quarters of the species. Members of these two families are represented on all habitable continents. All four families in the order have low-growing, herbaceous members; only the verbena group is noted for large trees. With some exceptions, plants of the Lamiales possess simple, opposite leaves; flowers with both stamens (male) and pistils (female); and two-lipped flowers in which one half (as viewed longitudinally) is the mirror image of the other (bilateral symmetry, or irregular flowers). Many genera of the Lamiaceae and the Verbeniaceae have distinctive, four-angled stems. Most of the roughly 3,200 species of the mint family are annual or perennial herbs. Their primary centre of distribution is the Old World, from the Canary Islands to the Himalayas, with lesser centres in Ethiopia, Madagascar, southern areas of Africa and India, Sri Lanka, and oceanic regions eastward. Centres of distribution in the New World range from the mountains in central Mexico into Argentina and Chile, with secondary centres radiating northward and eastward. Essential oils, which are used medicinally, for flavouring foods and beverages, and in perfumery, are derived from many genera of the mint family. The oils from horehound (Marrubium vulgare) and clary (Salvia sclarea) have medicinal value. Mentha cultivars (horticultural varieties) grown commercially for their oils are M. arvensis for menthol; M. gentilis and M. spicata for spearmint; and M. piperita for peppermint. Spice plants include marjoram (Origanum majorana), European marjoram (O. vulgare), sweet basil (Ocimum basilicum), sage (Salvia officinalis), savory (Satureja hortensis), lemon balm (Melissa officinalis), and thyme (Thymus vulgaris). Perfumes are derived from lavender (Lavandula angustifolia) and rosemary (Rosmarinus officinalis). Border, bedding, and ground cover plants of the mint family include Levendula, Mentha, and the so-called dead-nettle (Lamium maculatum), a semievergreen. Among the ornamental plants of Lamiaceae are species of Salvia that range in colour from blue to the orange-red Brazilian scarlet-sage (S. splendens). Bells-of-Ireland (Molucella laevis) develops an unusual, green, open-faced calyx much used in floral arrangements. Hundreds of named cultivars of Coleus, notable for their colourful leaves, are prized as houseplants and for protected outdoor plantings. Wildflowers and cultivated varieties of Monarda, the bergamots, are also appreciated for their colour in summer. The verbena, or vervain, family (Verbenaceae), composed of some 2,600 species, is distributed largely in tropical and subtropical South America and Africa. Other places of origin include central Asia, Japan, and islands near India; few members are native to Europe, Asia Minor, and North America. The most important commercial plant of Verbenaceae is Tectona grandis, the teak native to India, Myanmar (Burma), and Malaysia; it is also grown in other warm areas for its valuable wood. Another Asian tree, Vitex altissima, produces commercial timber; wood of the related V. divaricata is used for shingles and the bark for tanning. A related smaller tree, the aromatic V. agnus-castus (chaste tree) is a hardy ornamental in warm temperate regions. Fiddlewood ( Citharexylum fruticosum) of the West Indies, with the general appearance of a cherry tree, produces valuable timber and blossoms in all seasons. Species of Avicennia, the black mangrove, inhabit the coastal mud flats of Florida and many tropical lands. Their large seeds germinate while still attached to the parent plant. When released from the parent, the root of this seedling gets stuck in the mud and quickly grows into a new plant. In addition, numerous stilt roots and special roots growing upward from the watery soil permit the mangroves to literally invade the sea. Other notable plants of the Lamiales include the evergreen beautyberry (Callicarpa americana), lemon verbena (Aloysia triphylla), yellow sage (Lantana camara; see ), and Verbena hybrida, a desirable ground cover. The carpet bugleweed (Ajuga reptans of the Lamiaceae), native to Europe, spreads by stolons (above-ground runners), and A. pyramidalis produces rhizomes to form enlarged colonies vegetatively. Reproduction in the mint order is, however, accomplished most efficiently by seeds. The predominant inflorescence (flower cluster) is a raceme in which the lowest flowers of the branched system open first. Most genera produce bisexual flowers bearing both stamens and pistils. A representative flower is four- or five-parted, sepals are partially fused to form a bell-shaped calyx, and petals form a tubular corolla that is two-lipped. Typically two united carpels form the pistil, which consists of a basal ovary, a slender style, and the pollen-receptive stigma. After pollination and fertilization, the ovule becomes the seed and the ovary the fruit. The ovary in the Lamiales is deeply four-lobed with the style arising from the central depression. When mature, the fruit separates into four nutlets, a characteristic that distinguishes the mint family from most members of the Verbenaceae. Fruits in the verbena family may also split apart, but many are berries or drupes (outer layer fleshy, but inner one stony).