Wolffia borealis (Northern Watermeal)

Plant Info
Also known as: Spotted Watermeal
Family:Araceae (Arum)
Life cycle:perennial
Habitat:part shade, shade, sun; shallow quiet waters; moderate to hard water lakes, ponds, ditches, bog pools, slow-moving rivers
Bloom season:July - September
Plant height:.5 mm
Wetland Indicator Status:GP: OBL MW: OBL NCNE: OBL
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

Pick an image for a larger view. See the glossary for icon descriptions.

Detailed Information

Flower: Flower shape: indistinct

Flowers are rarely produced. When present, a single flower with a single style and a single stamen is in a cavity in the center of a leaf.

Leaves and stems: Leaf attachment: basal Leaf type: simple

[photo of plants] Plants have 1 or 2 leaves (known as fronds), usually unequal in size, each boat-shaped (when viewed from the side), flat across the top, elliptic to egg-shaped in outline, .7 to 1.5 mm long, 1.3 to 2 times as long as wide, rounded to blunt at the tip, with a pouch at the base from which young plants arise. Color is bright to dark green with 50 to 100 whitish stomates (pores) across the surface, giving a polka-dotted appearance. Plants have no stems and no roots and float on the water's surface.

Fruit: Fruit type: seed_without_plume

Fruit is rarely produced. When present, a flower may produce a single smooth, globular seed.


From the distribution map you can see that Wolffia is not well-documented in Minnesota, no doubt due at least in part to it's tiny size: it is considered the smallest flowering plant in the world and it's difficult to prepare herbarium specimens. The two Wolffia species in Minnesota are very similar but not that difficult to distinguish once you know the secret: Wolffia borealis leaves are elliptic to egg-shaped in outline, flat across the top, bright to dark green covered in tiny whitish stomates (pores), where Wolffia columbiana leaves are rounder, rounded across the top, and transparent green with only 1 to 10 stomates and a jewel-like sparkle under the surface. One observer thought W. borealis resembled a click beetle where W. columbiana was more like a jellybean. Maybe that helps (or not). Both species commonly grow together and with other duckweeds.

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More photos

Photos by Peter M. Dziuk taken in Ramsey and Washington counties.


Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: gary - Carlton County
on: 2021-04-17 15:56:34

I think I may have found a species of Wolffia near Scanlon several years ago. Now that the wetlands are thawed I should take a look.

Posted by: Dan Burns - Princeton
on: 2021-08-23 12:30:10

The sample I ventured to go down and get from one of the ponds east of the Rum River in Princeton looks like Spirodela as pictured here. If I might politely inquire, why is there no page for that? Or perhaps I'm using the wrong search parameters.

Posted by: K. Chayka
on: 2021-08-23 18:53:19

Dan, only about half the aquatics known to be in Minnesota are on the website as of this writing. They are all on the list of things-to-do. Patience is a virtue. :-)

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