Flower:

Plants rarely flower. Flowers are contained in lateral pouches near the base of the plant with a narrow opening at the top, usually 1 flower per plant, occasionally 2. Flowers lack petals or sepals, have 2 stamens and a single style.

Leaves and stems:

Leaves, known as fronds, float on the water's surface, are 1 to 4 mm (to ~1/6 inch) long, 1 to 1.5 times as long as wide, oval to inversely egg-shaped, widest at or above the middle, rounded at the tip, lack a stem and are faintly 3-veined. The upper frond surface is bright green and usually has a few pimple-like bumps (papillae) along the midvein.

The lower surface is green but often spotted or tinged red or purple. Attached towards the base of a frond is a single root up to 6 inches (15 cm) long, but usually much shorter. A plant has a single frond; 2 to several are often connected together though may eventually separate.

Fruit:

Like the rare flower, fruit—a tiny, ribbed seed—is rarely produced. Reproduction is primarily vegetative, via offshoots known as turions, which are round to kidney-shaped, lack roots, and initially green turning olive to reddish-brown. In the fall, turions drop off and sink to the bottom of the water where they overwinter, floating back up when temperatures warm in spring, then growing, developing roots, and starting the cycle over again.

Notes:

Turion Duckweed is very common in Minnesota and is found in the quiet waters of lakes, ponds, marshes, swamps, swales, sloughs and slow-moving streams, and is likely present in every Minnesota county. It's frequently mixed with Watermeals (Wolffia) and other Duckweeds (Lemna and Spirodela), forming large colonies that can cover the entire surface of a pond. It is typically identified by the turions produced in late summer, the red spotting or tinge on the underside of a frond, which is not always present or prominent, and the raised bumps on the upper surface, which can appear as a ridge when the light hits it right.

Spirodela polyrrhiza also has turions and is usually red-purple on the underside of fronds, but is easily distinguished by the larger fronds (to 8 mm) with 7 or more veins and multiple roots per frond. Lemna turionifera is most easily confused with Lemna minor, which can be somewhat larger (fronds up to 8 mm long) and lacks both the raised bumps on the upper surface (surface is mostly flat) and the turions, but it can be very difficult to distinguish them when turions are absent. Anita Cholewa, a curator at the Bell Herbarium (now retired) noted that most of the L. minor specimens were previously misidentified and are L. turionifera instead. We have photographed Duckweeds from dozens of locations around the state and I can't say with any confidence that Lemna minor was at any of those sites except for one.