Description from Flora of China
Herbs terrestrial, prostrate or erect. Stem smooth or 4-ribbed, glabrous to sparsely pubescent. Leaves decussate or alternate, rarely in whorls of 3(-5), petiolate or sessile, simple, margin serrate or entire; venation pinnate. Inflorescence an indeterminate spike of solitary flowers borne in axils of alternate, opposite, or whorled primary bracts, with lateral spikes in axils of upper leaves. Flowers bisexual, (3 or)4-merous. Sepals deltoid, often with midrib and median basal callus, persistent in fruit. Petals hooded, keeled, usually shortly clawed, caducous. Stamens usually 2 × as many as sepals; filaments short; anthers oblong, 4-loculed, antisepalous anthers slightly longer than antipetalous ones. Ovary incompletely (3 or)4-loculed, with 1 pendulous ovule per locule (if 2, then 1 aborting early), (6-)8-ribbed, ornamented, mid-sepaline ribs less distinctly raised than others; styles as many as sepals; stigma capitate. Fruit small, nutlike, 1-loculed (septa almost absent); pericarp somewhat membranous. Seed 1, occupying entire fruit.
In FRPS (53(2): 140-143. 2000), Gonocarpus was included in Haloragis J. R. Forster & G. Forster. However, the present treatment follows Orchard (Bull. Auckland Inst. Mus. 10: 1-299. 1975), who recognized Gonocarpus based on differences of the inflorescence, septa, pericarp, and development of the fruit.
About 35 species: SW Asia, and primarily Australia and New Zealand; two species in China.