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Subshrubs or perennial herbs, minutely hispid or glabrous. Leaves opposite or alternate, entire. Cymes terminal, becoming racemelike or paniculate, bracteate. Calyx 5-parted, becoming fastigiate or ovoid, base 5-veined or winged; lobes oblong to lanceolate, enlarged in fruit. Corolla broadly tubular, frequently tomentose inside; throat appendages usually absent; limb 5-parted; lobes triangular-ovate, apex caudate-attenuate. Stamens inserted on lower part of corolla tube; anthers oblong-linear to lanceolate, with awnlike and spiral-twisted connectives at apex. Ovary 4-parted. Style linear, exserted from corolla throat; stigma obscure. Gynobase fastigiate and 4-veined longitudinally. Nutlets dorsiventrally compressed, margin of abaxial surface protruding, becoming cupular, dentate. Seeds suborbicular.
Annual or perennial herbs, sometimes suffrutescent. Leaves alternate or opposite, sessile or stalked. Cymes loose, often many-flowered, usually with bracts that may be similar to the upper stem leaves. Flowers pentamerous. Calyx on distinct, often fairly long pedicels, strongly accrescent in fruit, lobes free to the base or united in part. Corolla more or less rotate to funnel-shaped with a short tube and long-acuminate to cuspidate lobes, without scales in the throat. Stamens: anthers subsessile in the tube, oblong to linear, with long sterile awns that are twisted round each other. Ovary not divided in flower; style filiform, stigma small, globose. Nutlets 4, ovoid, triquetrous or nearly globose, smooth or rugose, sometimes hairy, with or without a distinct margin. Fig. 14. Fig. 15.
Stamens sessile or subsessile, the filament absent or less than 1 mm. long and broader than long, the anthers oblong and inserted on the inner side of the connectives which are prolonged above the anthers, the whole androecium converging above to form a cone with the connective prolongations twisted together at the apex, the connectives with long shaggy hairs on their dorsal surface.
Fruit either of four smooth or variously ornamented nutlets attached to a pyramidal gynobase or (by abortion) of a single sessile nutlet (see note on sections below).
Sepals free to the base or loosely adherent along lower margins, usually ovate to lanceolate and rounded to cordate at the base, strongly accrescent in fruit.
Corolla campanulate to funnel-shaped, with ovate-acuminate to broadly triangular lobes which are often spreading or reflexed, without scales at the throat.
Flowers (calyx, corolla and stamens) 5-merous or occasionally some flowers in T. zeylanicum 6-merous.
Inflorescence either a bracteate one-sided cyme or a branching system of ebracteate very lax cymes.
Annual or perennial herbs to small shrubs, often with conspicuously tuberculate hairs.
Ovary 4-lobed, with straight gynobasic style, the stigma scarcely differentiated.
Lower leaves usually opposite or sub-opposite, upper ones usually alternate.
