PlantaeDB Logo
Login Sign-up

Genus Hydrocotyle in Family Araliaceae

In botanical taxonomy, a genus (plural genera) is a rank used to group closely related species within a family. In the hierarchy, genus sits below family and above species.

Genera are defined by shared morphological, anatomical, and genetic characteristics (for example, features of flowers, fruits, seeds, or leaves) that indicate a close evolutionary relationship among the species they contain.

Each genus can include one or more species. Examples include Rosa (roses) and Solanum (nightshades, including tomato and eggplant).

Do you wish to read more about plant taxonomy? Click here!

Genus Description

Suggest a correction!

Hydrocotyle (Tourn. ex L.) is a large, cosmopolitan genus in Araliaceae comprising approximately 190 species, with a strong concentration in tropical to warm-temperate zones of the Southern Hemisphere. The center of diversity lies in Australasia and the Pacific, with secondary hotspots in South America, Africa, and southern Asia; a notable radiation occurs in New Guinea and adjacent archipelagos. Plants typically occupy wet, often shade-rich sites from sea level to mid-elevations, including stream margins, swamps, marshes, moist forests, and lawns; several species are aquatic or amphibious. The type species for the genus is Hydrocotyle vulgaris L., fixed by Linnaeus in Species Plantarum (1753). In recent treatments, the former small northern-hemisphere H. americana is frequently placed in H. vulgaris, and the Asian H. polycephala has been segregated into the genus Cosmopolitanum (J. F. B. Ross et al., 2021), indicating active re-circumscription within the complex.

Hydrocotyle is easily recognized by its herbaceous, often creeping or stoloniferous habit and distinctive peltate leaf blades in many taxa (rarely basifixed). Indumentum is commonly a combination of simple, uniseriate trichomes and short, glandular hairs; stipules are usually present as membranous or membranous-ciliate scales fused into a sheath around the stem (ochrea-like). Inflorescences are simple or compound umbels borne on axillary peduncles, occasionally congested into heads; the involucral bracts form a persistent involucre. Flowers are small with sepals reduced or absent, five free white to greenish petals, five stamens, and a simple style; the inferior ovary is typically bicarpellate with two distinct styles. Fruit is a schizocarp, laterally compressed with five primary ribs; mericarps are dorsally ribbed and laterally flattened, with vittae (oil ducts) not consistently present, and the commissural surface is often smooth or ridged. Seeds have a small embryo and often a slight winged margin.

Pollination is largely undocumented in the wild, with insect visitation noted informally in some cultivated taxa, while dispersal appears to be primarily by water (hydrochory), aided by the buoyant fruits, occasional epizoochory through mud attachment, and anthropochory via garden or aquatic plantings. Chromosome numbers vary widely across the complex and remain insufficiently synthesized to support a firm base number.

Taxonomically, Hydrocotyle has historically fluctuated between Apiaceae and Araliaceae; molecular phylogenies and combined analyses place it unequivocally in Araliaceae (Plunkett et al., 2004; APG IV, 2016). Major sectional or subgeneric treatments exist but are incompletely tested across the full range, and several narrow endemics remain undersampled. The genus is closely related to Centella and forms part of the Mackinlayaceae–Araliaceae clade resolved in global analyses. Recent floristic work and phylogenomic studies have supported species reassignments, yet higher-level subdivision remains provisional (Smith et al., 2019).

Human relevance includes widespread horticultural use as groundcovers and pond-edge ornamentals; several species have become invasive outside their native ranges, notably H. ranunculoides in Europe and H. sibthorpioides in parts of North America and Australasia. No timber or major crop significance is recognized. Conservation concerns center on the many micro-endemic taxa in island systems and fragmented wetlands; incomplete mapping and assessment limit Red List coverage (POWO, 2024; WFO, 2024). Continued taxonomic integration, in situ conservation, and monitoring of invasive populations are priority needs.

Pick a Species to see its components: