GENTIANACEAE (the

See also:

• GENTIAN

gentian

See also:

• FAMILY

family)  , in botany, an order of Dicotyledons belonging to the sub-class Sympetalae or Gamopetalae, and containing about 750 species in 64 genera . It has a world-wide distribution, and representatives adapted to very various conditions, including, for instance, alpine plants, like the true gentians (Gentiana), meadow plants such as the British Chlora perfoliata (yellow-wort) or Erythraea Centaurium(centaury), marsh plants such as Menyanthes trifoliata (bog-bean), floating water plants such as Limnanthemum, or steppe and sea-coast plants such as Cicendia . They are annual or perennial herbs, rarely becoming shrubby, and generally growing erect, with a characteristic forked manner of branching; the Asiatic genus Crawfurdia has a climbing stem; they are often low-growing and caespitose, as in the alpine gentians . The leaves are in decussating pairs (that is, each pair is in a plane at right angles to the previous or succeeding pair), except in Menyanthes and a few allied aquatic or marsh genera, where they are alternate or radical . Several genera, chiefly American, are saprophytes, forming slender low-growing herbs, containing little or no chlorophyll and with leaves reduced to scales; such are Voyria and Leiphaimos, mainly tropical American . The inflorescence is generally cymose, often dichasial, recalling that of Caryophyllaceae, the lateral branches often becoming monochasial; it is sometimes reduced to a few flowers or one only, as in some gentians . The flowers are hermaphrodite, and regular with parts in 4's and 5's, with reduction to 2 in the pistil; in Chlora there are 6 to 8 members in each whorl . The calyx generally forms a tube with teeth or segments which usually overlap in the bud . The corolla shows great variety in form; thus among the British genera it is rotate in Chlora, funnel-shaped in Erythraea, and cylindrical, bell-shaped, funnel-shaped or salver-shaped in Gentiana; the segments are generally twisted to the right in the bud; the throat is often fimbriate or bears scales . The stamens, as many as, and alternating with, the corolla-segments, are inserted at very different heights on the corolla-tube; the filaments are slender, the anthers are usually attached dorsally, are versatile, and dehisce by two longitudinal slits; after escape of the pollen they some-times become spirally twisted as in Erythraza . Dimorphic flowers are frequent, as in the bog-bean (Menyanthes) . There is considerable variation in the size, shape and external markings of the pollen grains, and a division of the order into tribes and sub-tribes based primarily on pollen characters has been proposed .

The form of the

honey-secreting developments of the disk at the base of the ovary also shows considerable variety . The superior ovary is generally one-chambered, with Central figure and figs . 1-4 after Curtis, Flora Londinensis. two variously de- Gentiana Amarella . veloped parietal pla- centas, which occa- I, A small form, natural size. sionally meet, form- 2, Calyx and protruding style. ing two chambers; 3, Corolla, laid open. the ovules are gener- 4, Capsule, bursting into two valves, and ally very numerous showing the seeds attached to their and anatropous or margins. half - anatropous in 5, Floral diagram. form . The style, which varies much in length, is simple, with an undivided or bilobed or bipartite stigma . The fruit is generally a membranous or leathery capsule, splitting septicidally into two valves; the seeds are small and numerous, and contain a small embryo in a copious endosperm . The brilliant colour of the flowers, often occurring in large numbers (as in the alpine gentians), the presence of honey-glands and the frequency of dimorphy and dichogamy, are adaptations for pollination by insect visitors . In the true gentians (Gentiana) the flowers of different species are adapted for widely differing types of insect visitors . Thus Gentiana lutea, with a rotate yellow corolla add freely exposed honey, is adapted to short-tongued insect visitors; G . Pneumonanthe, with a long-tubed, bright blue corolla, is visited by humble bees; and G. verna, with a still longer narrower tube, is visited by Lepidoptera . Gentiana, the largest genus, contains nearly three hundred species, distributed over Europe (including arctic), five being British, the mountains of Asia, south-east Australia and New Zealand, the whole of North America and along the Andes to Cape Horn; it does not occur in Africa . Bitter principles are general in thevegetative parts, especially in the rhizomes and roots, and have given a medicinal value to many species, e.g .

Gentiana lutea and others .