NEPENTHALES

an order of carnivorous plants, belonging to the class Magnoliopsida, also called dicotyledon (characterized by two seed leaves). The order consists of three families: the Droseraceae, containing the sundews and the Venus's-flytrap; the Nepenthaceae, consisting of the Old World pitcher plants; and the Sarraceniaceae, containing the New World pitcher plants. All of the order's approximately 195 species have adapted to poor soil conditions. They have leaves that are ingeniously adapted as pitfalls and traps to capture insects, digest them, and absorb the nutrients. Exotic plant collections often include species of this order, but otherwise Nepenthales' members are of no economic value. The features that link the three families (in addition to the carnivorous habit) include simple and alternately arranged leaves, low numbers of perianth parts (sepals and petals) arranged in whorls, superior ovary (situated above the perianth), and seeds shed from a dry capsule. The family Droseraceae contains species with leaves modified as real trapsi.e., active mechanisms that clamp shut or coil about victims lured by nectar secretions and delicate odours. The family's members are mainly herbs found in bogs, damp heaths, and wet savannas and are distributed mainly in the Southern Hemisphere. They are divided into 4 genera and 103 species. The principal genus is Drosera (the sundews), with about 100 species. The Droseraceae are characterized by the presence of petals, separate stamens, bisexual flowers (stamens and pistil in the same flower), and a one-chambered ovary. An active trap of the sundew (Drosera capensis). Sensitive tentacles topped with red Drosera species are most numerous in Australia and adjacent areas and in southern Africa. Only a few species grow in eastern North America and Eurasia. Drosera species vary from several centimetres to 1 m (3 feet) or more in height. The smallest species often are hidden among the mosses in a sphagnum bog. The sundews of the Northern Hemisphere usually produce 1 to 20 erect flowers on a single flower stalk that rises from a rosette of basal leaves to a height of 1520 cm (68 inches). Each slender leaf is covered with several hundred tiny bristlelike tentacles, each of which is topped with a reddish knob (in reality a gland) that exudes a clear, sticky, mucilaginous liquid. This sea of glistening, honey-fragrant drops lures midges, gnats, mosquitoes, and other tiny insects, who alight on the leaves. The mucilage on the tentacles smears and smothers the insect, whose struggles stimulate further secretions of the sticky liquid. Within minutes adjacent tentacles bend slowly over onto the insect, who becomes hopelessly engulfed by a web of sticky stalks. After a few days to a week, digestion is completed and the leaf straightens out, resetting the trap, and the remains of the previous victim fall off or are washed or blown away. Active traps of the Venus's-flytrap (Dionaea muscipula), a carnivorous plant. If depressed Each of the three remaining generaDionaea, Aldrovanda, and Drosophyllumof the Droseraceae is noted for having only one species, for limited distribution, and for its habitat preference. Venus's-flytrap (Dionaea muscipula; see photograph), for example, is restricted to the coastal plain of the two Carolinas in the United States, where it grows along edges of ponds and wet depressions. Its leaves radiate at ground level from a short stem. The blade of each leaf consists of two lobes hinged to each other like the jaws of a steel trap and provided with spinelike teeth along the margins. Many nectar glands and bright red digestive glands cover the lobes' surface. Three pressure-sensitive hairs arise from the middle of each lobe. When touched two or more times within a short period of time, these hairs transmit a chemical message causing the two lobes to close together, trapping the insect. When stimulated, the trap springs shut with amazing speed, usually within half a second or less. The leaf's two lobes close tighter as the prey struggles; digestive glands exude enzymes that digest the insect's softer parts within about a week. A leaf dies after three or four trappings. The Nepenthaceae family is characterized by a relatively limited geographic range, woody climbers, absence of petals, unisexual flowers and plants, stamens united into a column, flower clusters capable of growing terminally, a four-chambered ovary, and the formation of unique pitchers. The single genus Nepenthes lends its name to the family and to the order. It encompasses 80 species native to rain forests of northern Australia, the Philippine Islands, Malaysia, and the Seychelles, with its centre of concentration on the island of Borneo. All of the species capture insects by means of pitcher-shaped leaves that function as pitfalls. The prey is attracted to the large showy leaves by nectar, and it slips from a treacherous lip into the pitcherlike hollow leaf, which in reality is a cistern of digestive liquid from which there is no escape. Passive traps of the slender pitcher plant (Nepenthes gracilis). The leaf blade narrows into The members of Nepenthes are woody vines of the Old World that climb over vegetation by means of modified leaves, which may attain a length of 1 to 3 m. The leaves possess a broadened linear base that elongates into a strong, slender tendril. This twining tendril becomes transformed at its tip into a pitcher that is held upright. The pitcher consists of a bulging tube with a slippery rim surrounding the top opening. An unhinged lid arches over the orifice. The underside of the lid and the rim of the pitcher are beset with nectar glands, and red markings on the outside of the pitcher are additionally attractive to potential prey. Insects that successfully negotiate the corrugated lip of the pitcher lose their footing on the crumbly, waxy surface lining the upper half of the pitcher's interior. They drop into the lower part of the pitcher, which is crowded with more than 6,000 digestive glands per square centimetre. The Sarraceniaceae (q.v.) family has 3 genera containing 15 species of low perennial herbs found in bogs and wet savannas of the Americas. The largest genus is Sarracenia, with eight or nine species found in the Atlantic coastal regions of North America. The plants consist of a basal cluster of leaves arising from a short, creeping rhizome. The hollow tubular leaves are shaped like urns, trumpets, or small pitchers. They are carefully constructed pitfalls that entrap insects lured to the mouth of the leaf by nectar-secreting glands and glistening surfaces. Downward-pointing hairs in the throat of the pitcher prevent the insect's escape, and the exhausted prey falls into the digestive liquor at the pitcher's bottom, where it is digested. Members of the Sarraceniaceae typically have five sepals, petals either five in number or absent, many separate stamens, bisexual flowers, and a three- or five-chambered ovary. The major means of reproduction among the Nepenthales is sexual. Small plants of this order produce solitary flowers, but, in the majority of species, inflorescences are up to 30 cm long and sometimes branched. The basic number of flower parts is five in the Droseraceae and Sarraceniaceae and four in the Nepenthaceae. Stamens may number up to 24. Carpels number three, four, or five to constitute a single pistil that is differentiated into an ovary, separate styles, and pollen-receptive stigmas. Seeds are much more numerous in the pitcher plants than in the sundews. Nectar, fetid odours, and bright colours attract many kinds of insects that effectively pollinate the Nepenthales. Following fertilization, the ovules become the seeds and the ovary the fruit. The dry capsule (fruit) splits open to release seeds. See also pitcher plant; sundew; Venus's-flytrap.