Wolffia is a genus of tiny free-floating aquatic plants in the family Lemnaceae (order Arales), widely known by the common names watermeal or rootless duckweed. The roughly eleven accepted species hold a remarkable distinction: they are the smallest flowering plants on Earth. An individual plant consists of a single frond — nearly spherical to cylindrical in shape, no larger than a grain of cornmeal — that lacks roots, airspaces, and veins entirely. Flowers are extremely rare and inconspicuous, arising from a small cavity on the upper surface of the frond; each flower consists of just one stamen and one pistil.
Reproduction is primarily vegetative. A mature frond develops a terminal conical cavity from which it budges off a daughter frond, allowing colonies to spread rapidly across the water surface. When flowering does occur, seeds can also be produced. Growth rates vary considerably among species, but the genus collectively holds records in plant biology: a clone of Wolffia microscopica has been documented with a doubling time of just 29.3 hours, the fastest recorded for any flowering plant.
Wolffia plants are cosmopolitan, occurring on still or slow-moving freshwater surfaces worldwide, often intermixed with related duckweeds such as Lemna and Spirodela. Despite their minute size, they are nutritionally noteworthy: W. microscopica is more than 20% protein by dry weight and contains a full complement of essential amino acids. Several species have historically been harvested and eaten as a vegetable across Southeast and South Asia, and the genus is attracting renewed interest as a sustainable, high-protein food and livestock feed source.
Distribution
Wolffia has a cosmopolitan distribution, occurring on freshwater surfaces across tropical, subtropical, and temperate regions worldwide. Plants typically float on still or slow-moving water, often forming dense mats alongside other duckweeds such as Lemna and Spirodela.
Ecology
Wolffia inhabits calm or slow-moving freshwater bodies and frequently co-occurs with other members of the family Lemnaceae, including Lemna and Spirodela. Their extremely rapid vegetative reproduction allows colonies to blanket the water surface quickly. The fastest-growing species (W. microscopica) can double its biomass in under 30 hours.
Cultural Uses
Wolffia plants have been collected from the water and consumed as a vegetable in parts of Asia for centuries. Wolffia microscopica in particular is notable for its high protein content — exceeding 20% of dry weight — and its richness in essential amino acids, drawing interest as a sustainable protein source for human nutrition and livestock feed.
Taxonomy Notes
Wolffia belongs to the family Lemnaceae within the order Arales (class Monocotyledons). Lemnaceae comprises the duckweed family, a group of highly reduced monocots whose members have lost most conventional plant organs. As of 2020, eleven species are accepted by Kew's Plants of the World Online. GBIF places the genus in Lemnaceae / Arales.
