Herbs perennial, rarely annual, aquatic or terrestrial, monoecious or dioecious. Stem creeping, ascending or erect, often rooting at lower nodes. Leaves estipulate, 2-4-whorled, decussate, or alternate, in terrestrial species always simple, in aquatic submersed species always pectinately lobed. Inflorescence an indeterminate or determinate spike of 1-5-flowered dichasia borne in axils of leaflike primary bracts; occasional lateral inflorescences simpler. Flowers minute, actinomorphic, epigynous, protandrous, anemophilous or entomophilous, bisexual or unisexual. Sepals (2-)4, but absent in female flowers of some Myriophyllum, mostly persistent. Petals alternisepalous, (2-)4, absent in female flowers of some Myriophyllum, imbricate, longer than sepals, often deciduous with stamens. Stamens 1 or 2 × as many as sepals; filaments short, slender; anthers basifixed, mostly oblong or linear, 4-loculed, dehiscing by slits, antisepalous anthers sometimes somewhat longer than antipetalous ones; pollen grains shedding at 3-celled stage. Ovary inferior, 1(or 2)- or 4-celled, septa solid or practically absent (present only at base and apex of ovary); styles as many (rarely half as many) as sepals, alternisepalous, free, mostly short, grading into globose or subulate stigmas, spreading in fruit; stigmatic papillae hairlike; ovules as many as styles, rarely 1, apical, pendulous, anatropous. Fruit nutlike or a drupe, variously ornamented with wings, ribs, and tubercles, indehiscent and 1-seeded or breaking up into (2-)4 1-seeded mericarps; pericarp membranous or endocarp woody; exocarp membranous or swollen and spongy. Seeds with thin testa; embryo cylindric, surrounded by thick, white albumen.
About eight genera and ca. 100 species: mainly S hemisphere, particularly Australia, but Myriophyllum cosmopolitan and Proserpinaca Linnaeus confined to the N hemisphere; two genera and 13 species (one endemic, one introduced) in China.
The spelling "Haloragidaceae" was used in FRPS, but the family name is conserved in Appendix IIB of the International Code of Botanical Nomenclature, where the spelling Haloragaceae is used.
Wan Wenhao. 2000. Haloragidaceae [sic]. In: Chen Chiajui, ed., Fl. Reipubl. Popularis Sin. 53(2): 134-143.