Habit and leaf form. Small, branched, creeping herbs; bearing essential oils. Plants succulent. Perennial (with prostrate, rooting stems emitting short, erect, leafy branches). Leaves opposite; leathery (the blades); petiolate (the petioles flattened); connate (by the petioles); obscurely gland-dotted; aromatic; simple. Lamina entire. Leaves exstipulate. Lamina margins minutely denticulate.
Reproductive type, pollination. Plants hermaphrodite.
Inflorescence, floral, fruit and seed morphology. Flowers solitary; terminal, or axillary; regular; 4 merous; cyclic; tetracyclic. Free hypanthium absent.
Perianth with distinct calyx and corolla; 8; 2 whorled; isomerous. Calyx 4; 1 whorled; gamosepalous; regular; imbricate (?); with the median member anterior. Corolla 4; 1 whorled; gamopetalous; sub- rotate; regular.
Androecium 4. Androecial members adnate (epipetalous); free of one another; 1 whorled. Androecium exclusively of fertile stamens. Stamens 4; isomerous with the perianth; oppositisepalous; alternating with the corolla members. Anthers dorsifixed; introrse. Pollen grains aperturate; 3 aperturate; colporate (colporoidate).
Gynoecium 2 carpelled (but ostensibly four, the carpels being deeply lobed, cf. Labiatae). Carpels isomerous with the perianth (ostensibly), or reduced in number relative to the perianth (?). The pistil 4 celled. Gynoecium syncarpous; eu-syncarpous; superior. Ovary 4 locular (ostensibly), or 2 locular (with four locellae via false septa, cf. Labiatae?). Locules secondarily divided by ‘false septa’, or without ‘false septa’ (?). Gynoecium stylate. Styles 1 (slender, long or short); ‘gynobasic’. Stigmas 1 (inconspicuous). Placentation basal. Ovules 1 per locule (ostensibly), or 2 per locule (if the apparent locules are interpreted as locelli); ascending; anatropous.
Fruit non-fleshy; a schizocarp. Mericarps comprising nutlets. Fruit of four one-seeded, setulose nutlets. Seeds copiously endospermic.
Geography, cytology. Antarctic. Temperate. New Zealand, Patagonia.
Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Lamiiflorae; Lamiales (?). Cronquist’s Subclass Asteridae; Lamiales. APG 3 core angiosperms; core eudicot; Superorder Asteranae; lamiid; Order Lamiales.
Species 2. Genera 1; only genus, Tetrachondra.