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Annual or perennial herbs. Stem erect or prostrate, often 4-angled. Leaves decussate or in false whorls, stipules connate with petioles forming a broad truncate tube, fimbriate, with marginal bristles. Flowers small or minute, in more or less congested dichasial cymes, often forming dense heads of up to 350 flowers subtended by 1-8 pairs of leaf-like bracts and often with filiform bracteoles. Hypanthium obconical or more or less cylindrical, pubescent above. Calyx tube more or less absent above hypanthium, lobes 2-8. Corolla infundibular or salver-shaped, lobes 4. Stamens 4, anthers included or exserted. Ovary 2-locular. Fruit a 2-valved capsule.

Key to the species

Serial Key Reference
1a. Stem erect or suberect 2
1b. Stem prostate, procumbent, decumbent or spreading 4
2a. Stem erect and glabrous 3
2b. Stem erect or suberect, stem angles more or less scabrid. Corolla white or pink, capsule glabrous or sparsely pubescent S. stricta
3a. Leaves simply opposite; flowers in terminal and axillary heads; corolla lobes much longer than tube S. ocymoides
3b. Fascicles of smaller leaves in axils; flowers in clusters in upper nodes, when terminal then heads subtended by 2 or 4 leaflike bracts S. verticillata
4a. Corolla pink or purplish pink; flowers in axillary clusters 5
4b. Corolla white, or mauve to blue, rarely white; inflorescence terminal or or from upper leaf axils 6
5a. Stem procumbent, hispid; stigma bifid; capsule hispid S. auriculata
5b. Stem prostrate, decumbent, densely hairy; stigma lobe linear; capsule finely reticulate warty S. latifolia
6a. Leaves linear to narrowly elliptic, hispid to pilose, margin somewhat callused; corolla mauve to blue, rarely white S. articularis
6b. Leaves narrowly elliptic-oblong to elliptic, scaberulous to glabrescent; corolla white S. prostrata