Botany (Fortieth Parallel), 297. 1871.
Herbs, perennial, suffrutescent, glabrous. Stems numerous from base, erect or prostrate, branched, ribbed, not jointed, not armed, not fleshy. Leaves opposite (rarely alternate), connate, clasping at base, sessile, succulent; blade linear or broadly ovate, margins entire, apex acute or apiculate. Inflorescences axillary, flowers solitary or in 2–3-flowered clusters, bibracteate. Flowers bisexual, with 1 or 2 bractlets ± equaling perianth length; perianth deeply 5[–7]-parted, segments strongly imbricate, chartaceous; stamens 5; stigmas 2. Fruiting structures: fruit a utricle; pericarp free from seed, membranous, indehiscent. Seeds vertical, lenticular; seed coat black, shiny; embryo annular, perisperm copious. x = 9.
w United States, Central America, South America.
Species ca. 5 (2 in the flora).