Habit and leaf form. Shrubs. Plants succulent, or non-succulent; unarmed. Leaves cauline. Plants with a basal concentration of leaves, or with neither basal nor terminal concentrations of leaves. Stems not ‘jointed’. Stem internodes solid. Helophytic to xerophytic. Leaves minute to large; opposite (mostly), or alternate and opposite; spiral, or distichous; fleshy; sessile; simple; epulvinate. Leaf blades entire; narrowly oblong, or ovate, or linear; pinnately veined; hastate, or sagittate, or attenuate at the base, or cuneate at the base. Leaves without stipules. Leaf blade margins entire. Leaves without a persistent basal meristem. Leaf anatomy. Hydathodes present, or absent. Hairs present; complex hairs absent. Branched hairs absent. Extra-floral nectaries absent.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in cymes. The terminal inflorescence unit cymose. Inflorescences axillary; flowers basally fused in pairs. Flowers sessile; ebracteate; ebracteolate; minute, or small; regular; cyclic. Hypogynous disk present, or absent. Perianth sepaline; 5; 1 -whorled; joined (imbricate); fleshy, or non-fleshy; persistent; accrescent, or non-accrescent. Calyx present; not replaced by accrescent bracteoles; (interpreting the perianth as such) 5; gamosepalous; shortly blunt-lobed; imbricate; non-fleshy; persistent (in the fruit); accrescent. The fruiting calyx not berrylike; winged. Calyx lobes short, broad, thick lobes. Corolla absent. Androecial members definite in number. Androecium 5. Androecial members free of the perianth, or adnate (to the base of the perianth); all equal; free of one another; 1 -whorled. Androecium exclusively of fertile stamens. Stamens 5; all more or less similar in shape; isomerous with the perianth; oppositisepalous. Anthers bent inwards in bud; dehiscing via longitudinal slits; tetrasporangiate. Gynoecium (2–)5 carpelled. The pistil 1 celled. Gynoecium syncarpous; synovarious to synstylovarious; superior. Ovary unilocular; 1 locular; sessile. Gynoecium stylate. Styles 2; partially joined. Stigmas 2. Placentation basal. Ovules in the single cavity 1; pendulous, or ascending; non-arillate; campylotropous.
Fruit and seed features. Fruit non-fleshy (pericarp membranous); indehiscent; capsular-indehiscent; 1 celled. Gynoecia of adjoining flowers combining to form a multiple fruit, or not forming a multiple fruit. Fruit 1 seeded. Seeds more or less non-endospermic. Perisperm present, or absent. Cotyledons 2. Embryo coiled, or curved, or bent.
Etymology. From the Greek didymos (double, twin) and anthos (flower); the flowers grow in pairs.