Pilea aquarum aka Pilea Aquarum

Pilea aquarum is a small perennial herb in the nettle family (Urticaceae), formally described by the British botanist Stephen Troyte Dunn in 1908 in the Journal of the Linnean Society. The species is native to subtropical southeastern China, with its range extending west to southeastern Sichuan and including the provinces of Guangxi and Guangdong; the World Checklist of Vascular Plants also records the species in adjacent areas of south-central China, and the Catalogue of Life Taiwan records its presence on Taiwan. Two infraspecific taxa are currently accepted: the typical Pilea aquarum subsp. aquarum and Pilea aquarum subsp. acutidentata.

The plant is a low-growing, stoloniferous herb that typically reaches only 10 to 30 centimetres in height. Its broadly elliptic to ovate-elliptic leaves are 1.5 to 6 centimetres long and 1 to 4 centimetres wide, with crenate (finely scalloped) margins and acute tips arranged in opposite pairs along the stems, as is characteristic of the genus Pilea. The species is dioecious or occasionally monoecious; male flowers are borne in a small cymose panicle 1.5 to 3.5 centimetres long, while the much smaller female flower clusters are less than 1 centimetre across. The Chinese vernacular name 湿生冷水花, literally "wet-habitat cold-water flower," reflects both its preference for moist or saturated ground and the species epithet aquarum, meaning "of waters."

In its native range, Pilea aquarum is a plant of damp subtropical sites, spreading clonally by stolons. The genus Pilea as a whole is described as comprising shade-loving herbaceous plants and shrubs distributed across tropical, subtropical, and warm temperate regions, and Pilea aquarum fits this pattern as a small understorey herb of moist forested habitats. Kew's automated extinction-risk model classifies the species as "not threatened" with a confident assessment, although it has not been formally evaluated by the IUCN Red List.

The species is essentially absent from mainstream horticultural literature. Major plant-finder databases such as the Royal Horticultural Society's plant finder, the Missouri Botanical Garden's Plant Finder, and Plants For A Future contain no record for Pilea aquarum, and no edible, medicinal, or other documented human uses appear in the consulted authoritative sources. It is not individually listed in the ASPCA's toxic and non-toxic plant database, although the ASPCA classifies many other species in the genus Pilea (for example Pilea cadierei, the aluminum plant) as non-toxic to dogs, cats, and horses.