Habit and leaf form. Shrubs, or herbs; without essential oils. Autotrophic. Annual, or perennial. Leaves basal, or cauline. Plants with neither basal nor terminal concentrations of leaves; to 2 m high. Helophytic, or mesophytic, or xerophytic. Leaves small to medium-sized; alternate and opposite (opposite on main stems and alternate on flowering stems); petiolate to subsessile (when opposite), or sessile (when alternate); non-sheathing; not gland-dotted; simple; epulvinate. Leaf blades dorsiventral, or isobilateral; entire; flat; linear to ovate; ovate, or oblong, or elliptic; cross-venulate. Mature leaf blades pubescent (hairs of 2 sizes, with a broad base), or glabrous (rarely). Leaves without stipules. Leaf blade margins entire. Leaves without a persistent basal meristem. Leaf anatomy. Hairs present, or absent. Urticating hairs absent. Stem anatomy. Secondary thickening developing from a conventional cambial ring.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Floral nectaries present. Nectar secretion from a circular nectary around ovary. Entomophilous.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’, or solitary (rarely); in cymes. Inflorescences simple. The terminal inflorescence unit cymose (coiled at first). Inflorescences terminal; with one to several erect, leafy, scorpioid cymes, with flowers loosely arranged; not pseudanthial. Flowers pedicellate; bracteate, or ebracteate; bracteolate; small; regular; 5 merous; cyclic; tetracyclic. Free hypanthium absent. Hypogynous disk present, or absent. Perianth with distinct calyx and corolla; 10; 2 -whorled; isomerous. Calyx present; 5; 1 -whorled; polysepalous, or gamosepalous (basally); if gamosepalous, lobed; imbricate, or open in bud, or valvate; persistent; accrescent. Sepals ovate. Calyx lobes ovate to linear. Corolla present; 5; 1 -whorled; gamopetalous; lobed. Corolla lobes about the same length as the tube. Degree of gamopetaly 0.5–0.8. Corolla imbricate, or contorted; rotate; regular; hairy abaxially, or glabrous abaxially; glabrous adaxially; white, or blue. Corolla lobes ovate. Androecial members definite in number. Androecium 5. Androecial members unbranched; adnate (to the corolla); all equal, or markedly unequal; coherent (by long hairs in a tube enclosing the style); 1 -whorled. Androecium exclusively of fertile stamens. Stamens 5. Staminal insertion in the throat of the corolla tube. Stamens becoming exserted; isomerous with the perianth; oppositisepalous; with sessile anthers, or filantherous. Filaments when present, very short and flat. Anthers connivent; dorsifixed to basifixed; dehiscing via longitudinal slits; introrse; tetrasporangiate; appendaged. The anther appendages apical (usually twisted at apex). Gynoecium 2 carpelled. The pistil 4 celled. Carpels reduced in number relative to the perianth. Gynoecium syncarpous; eu-syncarpous; superior. Ovary plurilocular (entire or scarcely 4-lobed); 2 locular (‘really’, but rarely ostensibly so), or 4 locular (ostensibly, via false septa). Locules secondarily divided by ‘false septa’. Gynoecium median; stylate. Styles 1; simple; from a depression at the top of the ovary; apical; not becoming exserted. Stigmas 1; capitate (minute). Placentation basal. Ovules differentiated; 2 per locule (i.e. per true locule), or 1 per locule (per cell, the gynoecium separating into one-ovuled portions); horizontal to ascending; epitropous; non-arillate; anatropous, or hemianatropous.
Fruit and seed features. Fruit aerial; fleshy, or non-fleshy; a schizocarp. Mericarps 4; comprising nutlets. Seeds endospermic, or non-endospermic. Cotyledons 2. Embryo straight, or curved.
Special features. Corolla tube straight.
Etymology. From the Greek for "hair" and "bond, cable"; the anthers have long hairs which form a spirally twisted beak.