Leaves are domed and 2 to 6 mm long. Top surface of the leaf is dull green or reddish brown. Bubble like clear cells can often be seen underneath the leaf.

Other Lemna.  Fat duckweed is not always fat - it can be flattened, but even so it should have visible large cavities in the fronds from above

Large cavities in fronds visible from above, or bubble like air cells underneath

Photograph showing large air cells underneath - take close-up side-on photos. 

Ponds, lakes, slow moving rivers and canals.

Summer and autumn.

Aquatic perennial.

Widespread in England and Wales as far north as Yorkshire, becoming less frequent further north.

Occasional and rather local in Leicestershire and Rutland. In the 1979 Flora survey of Leicestershire it was found in 35 of the 617 tetrads.