Lavender (Lavandula)

Description

Lavandula (common name lavender) is a genus of 47 known species of flowering plants in the mint family, Lamiaceae. It is native to the Old World and is found from Cape Verde and the Canary Islands, Europe across to northern and eastern Africa, the Mediterranean, southwest Asia to southeast India. Many members of the genus are cultivated extensively in temperate climates as ornamental plants for garden and landscape use, for use as culinary herbs, and also commercially for the extraction of essential oils. The most widely cultivated species, Lavandula angustifolia, is often referred to as lavender, and there is a color named for the shade of the flowers of this species. The genus includes annual or short-lived herbaceous perennial plants, and shrub-like perennials, subshrubs or small shrubs. Leaf shape is diverse across the genus. They are simple in some commonly cultivated species; in other species they are pinnately toothed, or pinnate, sometimes multiple pinnate and dissected. In most species the leaves are covered in fine hairs or indumentum, which normally contain the essential oils. Flowers are borne in whorls, held on spikes rising above the foliage, the spikes being branched in some species. Some species produce coloured bracts at the apices. The flowers may be blue, violet or lilac in the wild species, occasionally blackish purple or yellowish. The calyx is tubular. The corolla is also tubular, usually with five lobes (the upper lip often cleft, and the lower lip has two clefts). The most common form in cultivation is the common or English lavender Lavandula angustifolia (formerly named L. officinalis). A wide range of cultivars can be found. Other commonly grown ornamental species are L. stoechas, L. dentata, and L. multifida (Egyptian lavender). Because the cultivated forms are planted in gardens worldwide, they are occasionally found growing wild as garden escapes, well beyond their natural range. Commonly such adventitious establishment is apparently harmless at best, but in some cases Lavandula species have become invasive. For example, in Australia, Lavandula stoechas has become a cause for concern; it occurs widely throughout the continent, and has been declared a noxious weed in Victoria since 1920. It also is regarded as a weed in parts of Spain. Lavenders flourish best in dry, well-drained, sandy or gravelly soils in full sun. All types need little or no fertilizer and good air circulation. In areas of high humidity, root rot due to fungus infection can be a problem. Organic mulches can trap moisture around the plants' bases, encouraging root rot. Gravelly materials such as crushed rocks give better results. It grows best in soils with a pH between 6 and 8. Most lavender is hand-harvested, and harvest times vary depending on intended use.