Gentianaceae - Encyclopedia




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GENTIANACEAE (the gentian 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 Chloraperfoliata (yellow-wort) or ErythraeaCentaurium (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 dif ferent heights on the corolla-tube; the fila ments are slender, the anthers are usually attached dor 1 sally, are versatile, and dehisce by two longitudinal slits; after escape of the pollen they sometimes become spirall y twisted as in Erythraea. 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 subtribes 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 two variously developed parietal placentas, which occasionally meet, forming two chambers; the ovules are genervalves, 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 and 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 the vegetative parts, especially in the rhizomes and roots, and have given a medicinal value to many species, e.g. Gentiana lutea and others.

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