Greater Duckweed

Spirodela polyrhiza

The floating plant everybody knows: flat green discs the size of a fingernail that cover the surface in days. Useful for shade and for stripping nutrients from the water — and almost impossible to get rid of afterwards.

Light: low
Difficulty: easy
Height: 3 – 5 cm (1.2 – 2 in)
Temperature: 4 – 35 °C (39 – 95 °F)

Leaf colour: green, red
Plant type: floating
Growth rate: fast
CO₂ demand: low
Tolerates light: medium – high
Carbonate hardness: 2 – 30 °dKH
Placement: surface
Propagation: fragmentation
Grows emersed: yes

Appearance

Round flat fronds 0.5–1 cm across, green above and dark red beneath, with a few short roots hanging under each. They join into a dense mat on the surface.

Keeping

Nothing is needed at all: any light, any water, no substrate. The real question is how to keep it in check — it doubles in days, blocks light to plants below and clogs the filter intake. Scooping out most of it is a weekly job, and a few fronds are enough to start it all over.

Placement

On the surface. It suits tanks with shy fish and fry, and shades plants that dislike bright light. In a display tank it is usually more trouble than it is worth.

Propagation

By itself, splitting: each frond buds off new ones. Nothing needs to be done.

Water conditions match

The water suits 1043 of 1249 species in the catalogue — these are the ones people look up most often.

Swordtail Guppies Cobra Guppy Blood Red Molly Butterflyfish Red Zebra Cichlid Julii Corydoras Featherfin Synodontis Red-finned Parotocinclus Gastromyzon monticola Egg-shaped Goldfish Flame Tetra Gardner's Killifish African Tetra Kenyi Cichlid Cuckoo Catfish Golden Swordtail Hypsolebias picturatus Common Zacco Labeo Bicolor Gambusia Flying barb Gastromyzon scitulus Albino Zebra Danio Geophagus Brokopondo

Will eat this plant

These species damage plants, especially when their diet is short of vegetable food.

Bengal Loach Zebra Loach Burmese Border Loach Emperor Botia Spined Loach Marbled Headstander Pellegrin's Leporinus Leporinus striatus False Black Tetra Common Metynnis Mylossoma duriventre Red Whiptail Catfish Molly sphenops Balloon Molly Lyretail Molly Marble Molly Hi-Fin Platy Hawaii Platy Blue Platy Pintail Platy Black Platy Chocolate Molly Moonlight Gourami Melanotaenia parva

Matching water does not mean the fish will leave the plant alone.

The same plant with a different look: light, water and care are shared with the species.

Other varieties: Spirodela polyrrhiza

Scientific and other names, conservation status

Other scientific names: Lemna polyrhiza L., Spirodela polyrrhiza, Lemna bannatica, Lemna major, Lemna maxima, Lemna obcordata, Lemna orbicularis, Lemna orbiculata, Lemna polyrhiza, Lemna polyrhiza concolor, Lemna thermalis, Lemna transsilvanica, Lemna umbonata, Lenticula polyrrhiza, Lenticulata polyrhiza, Spirodela atropurpurea, Spirodela maxima, Spirodela polyrhiza masonii, Telmatophace orbicularis, Telmatophace polyrhiza, Thelmatophace orbicularis, Thelmatophace polyrhiza
Spirodela polyrhiza: (L.) Schleid.
Family: Araceae
Conservation status: LC

Greater Duckweed

Tank conditions

Care and keeping