RUBIACEAE, in botany, a large family of seed plants, be longing to the series Rubiales of the subclass Sympetalae (Gamo petalae) of dicotyledons, and containing about 450 genera with about 5,500 species. It is mainly a tropical family of trees, shrubs and herbs, but some of the tribes, especially Galieae, to which the British representatives belong and which contains only herbs, are more strongly developed in temperate regions; some species of Galium reach the Arctic zone.
The most striking characteristic of the family are the opposite decussate, generally entire, stipulate leaves. The stipules are very varied in form; they generally stand between the petiols of a pair of leaves (interpetiolar). The two stipules of adjacent leaves are usually united, and in the Galieae, as well shown in the British species, are enlarged and leaf-like, forming with the two leaves an apparent whorl ; by fusion or branching of the stipules the number of leaves in the whorl varies from four to eight or more. The flowers are mostly arranged in cymes or panicles or crowded into heads, and are frequently showy. The flowers are hermaphrodite and regular with parts in fours or fives; the four or five sepals, petals and stamens are placed above the ovary, which consists of two carpels and is crowned by a simple style usually ending in a head or in two lobes. The sepals are often small, sometimes re duced to a narrow ring encircling the top of the ovary or alto gether absent. The united petals form a corolla which varies widely in form in the different genera ; it is often funnel- or sal ver-shaped. The stamens are fixed to the corolla-tube and alter nate in position with its segments; the flowers are often dimorphic (or heterostyled) with short-styled and long-styled forms.
The fruit also varies widely in form and is dry or fleshy. When dry it forms a capsule with septicidal or loculicidal dehiscence or is a schizocarp separating when dry into two one-seeded meri carps which, as in the British cleavers (Galium Aparine), some times bear hooked appendages which aid their dispersal.
The family is divided into a large number of tribes based on the number of ovules in each ovary-chamber, the character of the fruit seed and ovule, and the aestivation of the corolla. These may be arranged in two classes as follows:— Cinchonoideae, often woody plants with scale-like stipules, and numerous ovules in each ovary-chamber; the fruit is generally a capsule. To this belong Cinchona (q.v.), a genus of large trees with handsome flowers containing about 4o species in the Andes of South America—it is well known as a source of quinine. An allied genus, Bouvardia (q.v.), is cultivated for its flowers.
Coffeoideae, often woody or shrubby plants with scale-like stip ules ; each ovary-chamber contains only a single ovule. Coffea, a genus of shrubs with about 45 species in the Old World tropics, includes the coffee plant (C. arabica and C. liberica) ; the fruit is a two-seeded drupe, the seed is the "coffee-bean." The thickened root of Uragoga Ipecacuanha yields ipecacuanha. In this class is the tribe Stellateae, herbaceous plants with leaf-like stipules; each ovary-chamber contains one ovule only. Includes the four British genera: Rubia, one species of which, R. tinctorum, is madder; Galium, including G. verum (lady's bedstraw), G. Aparine (goose-grass or cleavers), and other British species; Asperula, including A. odorata (woodruff) and Sherardia.
The most common representatives in eastern North America are Galium (cleavers, goose grass, wild licorice, etc.), Houstonia (bluets, innocence), and Mitchella (partridge berry). In western North America, in addition to a few species of Galium, the genus Kelloggia is very characteristic.