Flower:

Raceme of 1 to 9 small, pale yellow, snapdragon-like flowers on a naked stem extending 1 to 5 inches above the water. Flowers are about ¼ inch long, the lower lip extending horizontally, about twice as long as the upper lip, and its sides folded down. At the base of the lower lip is an inflated pouch about half as long as the lip. Red venation is generally present on the lower lip, a few faint streaks on the sides near the base and darker lines on the pouch.  

A well-defined spur is absent, with just a nub forming at the base of the lower lip. The 2 small sepals behind the flower are about equal in size, broadly egg-shaped with blunt tips. At the base of the flower stalk is a scale-like bract. Flower stalks, sepals and bracts are typically reddish brown.

Leaves and stems:

Leaves are alternate, semicircular to nearly round in outline, less than 2/3 inch in diameter, palmately divided near the base typically 3 or 4 times (up to 6), the sections flattened though may appear thread-like, and the primary divisions each forked 2 to 11 times. Bladders can occur on all leaves.

Underwater stems may produce turions (overwintering vegetative buds) at the tip. Part of the stem is generally integrated in the substrate and other part floats near the surface of the water.

Fruit:

 Fruit is a round capsule about 1/8 inch in diameter.

Notes:

Lesser Bladderwort is one of the more common and easy to identify species. It is circumboreal, and its presence has been known in Minnesota since at least the late 1800s. When in bloom, it can easily be identified by noting the longer lower-lip, obscure spur, and pale yellow flower color. When not in bloom it could be confused with Flat-leaved Bladderwort (U. intermedia), which has very similar leaves but larger, up to ¾ inch diameter, and its bladders are on specialized, leafless branches. The palmately divided and forked leaves distinguishes U. minor from Hidden-fruit Bladderwort (U. geminiscapa) and Common Bladderwort (U. vulgaris), both of which have branching and forked leaves, not palmately divided at the leaf base. The leaves of Humped Bladderwort (U. gibba) only fork one or two times. Although the commonly held view is that the bladders of bladderworts are for capturing and digesting microorganisms that provide the plant with nutrients, bladders more often have been observed to contain communities of microorganisms (bacteria, algae, and diatoms) living in the bladders, not as prey, suggesting that the bladders may also, and perhaps more importantly, serve to establish mutually beneficial relationships with some microorganisms.