Shrubs, subshrubs, or perennial herbs, not rarely clambering or climbing vines or rarely lianas, unarmed; stems often prickly and/or longitudinally ribbed or winged. Raphides present. Leaves opposite and with interpetiolar, triangular or ovate, persistent to caducous (Rubia siamensis) or reduced (R. tibetica) stipules or with leaflike stipules in whorls of 4, 6, to many in middle stem regions; domatia none; main veins single or 3-5(or more) and then palmate, secondary veins lateral. Inflorescences thyrsoid, with terminal and/or axillary cymes, usually paniculiform and often expanding from new axes developing with age; individual cymes few to many flowered, pedunculate, bracteate. Flowers pedicellate or sessile, rather small, usually bisexual and monomorphic, rarely polygamo-dioecious (R. cordifolia). Ovary inferior (hypanthium), ellipsoid, subglobose, 2-celled, ovules 1 in each cell, erect, axile. Calyx limb reduced and obsolete. Corolla white to cream, yellow, greenish or red to purplish, often turning black when dried, mostly rotate, but rarely also campanulate to funnel-shaped, inside glabrous or infrequently papillose; lobes predominantly 5 (rarely also less or more), valvate in bud, often long acuminate. Stamens usually 5, inserted at corolla base (or tube), exserted; filaments developed to reduced; anthers dorsifixed. Stigmas 2-lobed, included or exserted. Fruit developing into 2 separate or (by reduction) into only 1 subglobose, baccate, berrylike mericarp with fleshy meso- and endocarp, dark red, purple, black, or infrequently orange (R. cordifolia), glabrous or somewhat hairy; seeds ("pyrenes") 2, ellipsoid, subglobose, or plano-convex, with membranous testa; endosperm corneous; embryo subincurved; cotyledons leaflike; radicle prolonged, basiscopic.
Ovary bilocular, one ovule in each chamber, crowned by a minute disk; style branches 2, joined below; stigmas capitate.
Corolla rotate to subcampanulate, greenish, yellowish green to yellow; lobes ± triangular, (long) acuminate.
Leaves in whorls of (3)4–8(12), petiolate (in the Flora Zambesiaca area), blades cordate or broadly ovate, ovate-lanceolate to linear, rounded to ± cordate at base or narrowed to base, with 1–5(7) prominent veins.
Stems branched, 4-angled, ± brittle, mostly beset with recurved prickles.
Flowers in axillary and/or terminal cymes, hermaphrodite, 5 (rarely 4 or 6) -merous.
Scrambling, creeping or climbing perennial herbs, somewhat woody near the base; roots quite woody, reddish (yielding a red dye).
Fruit fleshy, glabrous, consisting of 2 round mericarps, each with a single seed, round on dorsal side, plane to convex on ventral side; one mericarp often aborted.
Herbs, the stems sometimes woody towards the base, often stiffly hairy or with tiny prickles
Leaves in whorls of 4–6(–8), some of which may be stipular in origin; blades linear, lanceolate, obovate or less often cordate, often prickly
Flowers small, in axillary and/or terminal cymes, hermaphrodite
Ovary 1–2-locular; ovules solitary in each locule, erect, affixed to the septum, amphitropous; style 2-fid or styles 2, short; stigmas capitate
Fruit fleshy, of 2 parts or rarely 1-locular
Seeds suberect, with plane or concave ventral face, horny endosperm and membranous testa, adhering to the pericarp.
Calyx-tube ovoid or globose, the limb obsolete
Corolla rotate or subcampanulate, (4–)5(–6)-merous
Stamens inserted in the corolla-tube, the anthers exserted