Columbia watermeal

Wolffia columbiana · Aquatic plants

A stand of it · Photo: Kallum McDonald / CC0

NativeFree-floating

Also called Watermeal, Wolffia

How to identify Columbia watermeal

Tiny round grains about 1/32 inch, like cornmeal on the water
No roots
Globe shaped, floating with only a small part above water
Feels gritty when rubbed between fingers

Similar plants

Duckweeds are larger, flat and have roots, northern watermeal has a flat dotted upper surface, and planktonic algae make the water itself green.

Growth profile

Growing season	Increases slowly in spring, explodes in mid to late summer, and overwinters as dense resting buds on the bottom.
Starts growing	About 60 F water; rapid in warm summer water
Light	Full sun
Depth	Surface of still water of any depth
How it spreads	Budding fronds; carried by birds and equipment
Habitat	Warm, quiet, nutrient rich ponds, often mixed with duckweeds.

Why it matters in a lake

Can build a thick floating layer that shades the pond and lowers oxygen, often after duckweed is present. It is one of the smallest flowering plants in the world.