GENTIANALES

gentian order of flowering plants, belonging to the class Magnoliopsida (the dicotyledons). It is composed of 6 families and approximately 5,500 species, although up to 11 families and 12,000 species have been recognized, depending on the classification used. Four large families account for most species and are important as the source of ornamental plants, drugs, and, to a lesser extent, fibres and rubber. Trees, shrubs, and vines are more characteristic of this order than are annual or perennial plants. The majority of species are native to the tropics or warmer temperate regions; only the gentian family (Gentianaceae) is found mainly in the North Temperate Zone. Most members of the Gentianales inhabit forests where humidity is high and soil composition favourable for growth. The members of the gentian order have a leaf blade that is a single unit (simple) and leaves that are opposite (two per node or joint). Some members secrete sticky substances from glandular appendages or the stipules. The flowers are usually showy, alike in size and shape (regular), and the petals are usually fused. The carpels are normally united to form a compound ovary that is positioned above the flower petals. The flowers contain multiple stamens. Ovules possess one integument (early stage of seed coat), and the nucellus (the nutritive tissue beneath the integument) is one-layered. The fruits are usually capsules or follicles), contain numerous seeds, and are winged or comose (tufted) to aid in wind-dispersal. The Loganiaceae, a largely tropical family, contains about 21 genera and at least 500 species. Seeds of the 40-foot (12-metre) tree of south Asia, Strychnos nux-vomica, yield the alkaloids strychnine and brucine. The former is a poison often used to kill rodents, and the latter is an additive in lubricants. Alkaloids produced by S. ignatii, the Saint-Ignatius'-bean of the Philippines, have been used to treat cholera. S. spinosa of southern Africa produces a yellow berry with edible pulp. S. toxifera is a source of curare. About 70 species of Loganiaceae are ornamentals. Latex tubes in the stems of the dogbane family, Apocynaceae, produce a milky juice (a feature shared with the milkweed family, Asclepiadaceae). Up to 200 genera and 2,000 species have been attributed to the Apocynaceae, although one classification places the numbers closer to 155 genera and 1,000 species. Most are shrubs or trees of tropical or subtropical regions. At least 33 genera are under cultivation. Members of Apocynaceae include the common oleander, the periwinkle (Vinca minor), and Funtumia elastica (grown specifically for its rubber-producing latex). The milkweed family, Asclepiadaceae, is characterized by specialized, oblong pollen masses (the pollinia) and by latex in all vegetative parts. Its 250 genera and 2,000 species have a wide distribution, particularly in the tropics. The floss of the milkweed seed has been used as a low-grade substitute for kapok and is useful for insulation. Many members of the Asclepiadaceae are ornamental. They include the butterfly weed (Asclepias tuberosa) and the waxplant (Hoya carnosa). Many cultivars of the cactuslike carrion flower Stapelia, an African succulent, are available. Petals of many species are foul-smelling and yellowish, with bands of darker colours. Flowers of certain members of the gentian family, or Gentianaceae, display some of the purest blues in the plant kingdom. This family of 75 genera and 1,100 species is composed of herbs distributed chiefly in North Temperate regions. Many gentians favour wet woods and meadows as habitats; others favour rocky, alpine conditions. Their tubular corollas vary from wide-open to bell forms and to completely closed ones. Gentiana lutea of Asia Minor is prized for its yellow flowers; its root is locally considered medicinal and is used to flavour vermouth. In all families of this order, seeds are produced in great profusion and are the most effective method of reproduction. The Indian hemp (Apocynum) and several milkweeds, however, form colonies by means of rhizomes, from which new plants arise to propagate the species vegetatively. In most genera, clusters of flowers (inflorescences) are arranged on somewhat elongated stems. The eventual form depends on the amount of branching and the length of stalk of each flower. Nearly flat-topped clusters are the general rule, with the oldest flower at the top or toward the centre. A representative flower of the gentian order will have parts in fours or fives. Following pollination and fertilization, the ovule becomes the seed and the ovary the fruit. In some families, the fruit ripens dryas a capsule in gentians or as a one-carpel unit (the follicle) in milkweeds. Fruits in the logania family ripen as either fleshy berries or drupes (with stony internal layer). Berries of coffee are representative of many madders.