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Annual or perennial herbs or subshrubs, with erect, straggling or procumbent stems. Leaves very variable, mostly small, linear to round, paired or in whorls of 3 or pseudo-verticillate, sessile or shortly petiolate; stipules connate with the petiole to form a sheath, divided into ± linear segments. Flowers small, hermaphrodite, not dimorphic, paired, arranged in short to long spikes or dense heads or combinations of both. Calyx-tube ovoid or angular; lobes 5, 1–3 foliaceous, much larger than the rest and resembling the leaves of the species concerned, or 1–2 foliaceous, 1–2 smaller foliaceous and the remainder in each case reduced to minute teeth or bristles. Corolla-tube mostly filiform, less often narrowly funnel-shaped; lobes 4–5, ovate to narrowly lanceolate; throat glabrous or in one species densely hairy. Stamens 4–5, well exserted, the filaments glabrous or less often hairy or with hairy projections. Ovary bilocular, the ovules solitary in each locule, erect, attached to the partition very close to the base; style glabrous, filiform, well exserted; stigma bifid (rarely 3-fid), the lobes filiform. Fruit ovate, subglobose or oblong, usually splitting into 2 (rarely 3) cocci one of which is crowned by the persistent foliaceous calyx-lobe or lobes. Seeds black, granulate, subglobose, ovoid or oblong, depressed ventrally, convex dorsally, sometimes slightly keeled mid-dorsally and with a round, oval or linear depression surrounding the hilum corresponding to the shape of the seed.