Wolffia arrhiza(L.) Horkel ex Wimm.

Rootless Duckweedrootless duckweedspotless watermeal

WFO wfo-0000334448 Accepted WFO 2026-06 8 photographs CC BY / CC BY-SA

Plate 1 figs. a–h · 8 separate observations

Wolffia arrhiza, photographed by Christian Berg
fig. a Christian Berg, CC BY 4.0 / 2022-05-11 / obs. 198314099
Wolffia arrhiza, photographed by Марина Садыкова
fig. b Марина Садыкова, CC BY 4.0 / obs. 154173601
Wolffia arrhiza, photographed by Vicente Lopes
fig. c Vicente Lopes, CC BY 4.0 / obs. 151696414
Wolffia arrhiza, photographed by Grzegorz Grzejszczak
fig. d Grzegorz Grzejszczak, CC BY-SA 4.0 / obs. 53506487
Wolffia arrhiza, photographed by Grzegorz Grzejszczak
fig. e Grzegorz Grzejszczak, CC BY-SA 4.0 / obs. 53261476
Wolffia arrhiza, photographed by Grzegorz Grzejszczak
fig. f Grzegorz Grzejszczak, CC BY-SA 4.0 / obs. 52329502
Wolffia arrhiza, photographed by Grzegorz Grzejszczak
fig. g Grzegorz Grzejszczak, CC BY-SA 4.0 / obs. 48305099
Wolffia arrhiza, photographed by Grzegorz Grzejszczak
fig. h Grzegorz Grzejszczak, CC BY-SA 4.0 / obs. 52394558

Every figure is a research-grade observation under CC0, CC BY or CC BY-SA, rehosted with the photographer’s name, the licence and the observation it came from. Photographs under a NonCommercial licence are excluded from this site and are never stored, which costs us a great many pictures and is not negotiable.

Native range 59 botanical countries

Regions where Wolffia arrhiza is native: Algeria, Angola, Benin, Botswana, Burundi, Canary Is., Cape Provinces, DR Congo, Ethiopia, Free State, Ghana, Guinea-Bissau, Ivory Coast, Kenya, KwaZulu-Natal, Madagascar, Morocco, Mozambique, Nigeria, Northern Provinces, Rwanda, Senegal, Tanzania, Togo, Tunisia, Uganda, Iran, Korea, Lebanon-Syria, North Caucasus, Taiwan, Transcaucasus, Bangladesh, India, Philippines, West Himalaya, Austria, Baltic States, Belgium, Bulgaria, Central European Russia, Corse, Czechia-Slovakia, East European Russia, France, Germany, Great Britain, Greece, Hungary, Italy, Netherlands, NW. Balkan Pen., Poland, Portugal, Romania, Sicilia, South European Russia, Spain, Ukraine AlgeriaAngolaBeninBotswanaBurundiCape ProvincesDR CongoEthiopiaFree StateGhanaGuinea-BissauIvory CoastKenyaKwaZulu-NatalMadagascarMoroccoMozambiqueNigeriaNorthern ProvincesRwandaSenegalTanzaniaTogoTunisiaUgandaIranLebanon-SyriaNorth CaucasusTaiwanTranscaucasusBangladeshIndiaPhilippinesWest HimalayaAustriaBaltic StatesBelgiumBulgariaCentral European RussiaCorseCzechia-SlovakiaEast European RussiaFranceGermanyGreeceHungaryItalyNetherlandsNW. Balkan Pen.PolandPortugalRomaniaSiciliaSouth European RussiaSpainUkraine Canary Is.Korea
Native distribution of Wolffia arrhiza, after Kew’s World Checklist of Vascular Plants. Introduced, extinct and doubtful records are excluded, so this is where the plant is from, not everywhere it now grows. Regions too small to draw at this scale are marked with a dot.
RegionTDWG codeContinent
Algeria ALG AFRICA
Angola ANG
Benin BEN
Botswana BOT
Burundi BUR
Canary Is. CNY
Cape Provinces CPP
DR Congo ZAI
Ethiopia ETH
Free State OFS
Ghana GHA
Guinea-Bissau GNB
Ivory Coast IVO
Kenya KEN
KwaZulu-Natal NAT
Madagascar MDG
Morocco MOR
Mozambique MOZ
Nigeria NGA
Northern Provinces TVL
Rwanda RWA
Senegal SEN
Tanzania TAN
Togo TOG
Tunisia TUN
Uganda UGA
Austria AUT EUROPE
Baltic States BLT
Belgium BGM
Bulgaria BUL
Central European Russia RUC
Corse COR
Czechia-Slovakia CZE
East European Russia RUE
France FRA
Germany GER
Great Britain GRB
Greece GRC
Hungary HUN
Italy ITA
Netherlands NET
NW. Balkan Pen. YUG
Poland POL
Portugal POR
Romania ROM
Sicilia SIC
South European Russia RUS
Spain SPA
Ukraine UKR
Iran IRN ASIA-TEMPERATE
Korea KOR
Lebanon-Syria LBS
North Caucasus NCS
Taiwan TAI
Transcaucasus TCS
Bangladesh BAN ASIA-TROPICAL
India IND
Philippines PHI
West Himalaya WHM

Not drawn on the map: Great Britain. We hold no public-domain boundary for this region, so it is listed rather than guessed at.

Region boundaries approximated from Natural Earth (public domain) and mapped to TDWG World Geographical Scheme for Recording Plant Distributions (WGSRPD) level-3 botanical countries (Brummitt 2001). Indicative, not the official WGSRPD geometry.

Where it actually grows measured, from 314 observations

Condition 5th percentile Median 95th percentile
Coldest month, mean daily low -12.2 °C -6.8 °C 3.9 °C
Warmest month, mean daily high 22.4 °C 23.8 °C 27.2 °C
Annual rainfall 528 mm 654 mm 1,041 mm
Rainfall in the driest quarter 63 mm 108 mm 151 mm

It is found where winters bring hard frost. This is not care advice and it is not a forecast. It is a measurement: we sampled the climate at every one of the 314 research-grade observations of Wolffia arrhiza that carry a coordinate, and this is the range those places actually span. The 5th and 95th percentiles are used rather than the minimum and maximum, because a single cultivated specimen in a heated conservatory should not widen a tropical plant's range to the Arctic.

This is not a hardiness zone. A USDA zone is the average annual extreme minimum temperature. The figure above is the mean daily minimum of the coldest month, which is a different quantity and is typically far warmer. Reading one as the other would place a plant several zones too warm, so we do not publish a hardiness zone, because we do not have one.

Also published as 8 synonyms

A synonym is not an error. It is a record of botanists disagreeing, in print, about where this plant belongs. Each of these was somebody’s considered answer.

  • Bruniera vivipara Franch.
  • Horkelia arrhiza (L.) Druce
  • Horkelia arrhiza Druce
  • Lemna arrhiza L.
  • Lemna microscopica Schur
  • Lenticula arrhiza (L.) Lam.
  • Wolffia delilii Miq.
  • Wolffia michelii Schleid.

Sourcesevery claim on this page

  1. World Flora Online Plant List. accepted name, authority, classification. CC0. Retrieved 2026-07-12.
  2. iNaturalist. photographs and flowering annotations, CC0 / CC BY / CC BY-SA only. per photograph. Retrieved 2026-06-27.
  3. Wikidata. common name (P1843), joined on the World Flora Online identifier (P7715). CC0. Retrieved 2026-07-13.
  4. Kew, World Checklist of Vascular Plants (WCVP v16). native distribution by TDWG level-3 botanical country, and life form. CC BY 3.0. Retrieved 2026-06-04.

We publish what we can source and we say so when we cannot. This page has no care advice and no toxicity claim, because we do not yet have those from a source we can cite.