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Wisconsin Plant of the Week

Utricularia vulgaris L.

Lentibulariaceae (Bladderwort Family)

Common Name:

common bladderwort


Wisconsin has eight species of bladderworts -- carnivorous perennial plants of wet and aquatic sites with flowers that resemble snapdragons.  Common bladderwort -- much more common than any of the other species -- is a free-floating plant found in shallow still water of ponds and marshes. Patches can cover large areas with emergent bright yellow flowers in July and early August.

Its floating leaves are alternate and finely branched. The leaf segments are round in cross section and become progressively thinner with each branching. The leaf segments carry small bladders, about 3 mm across, that trap prey like mosquito larvae and protozoans.  Initially the bladders are transparent and they turn dark with age.

The bladders have glands inside that absorb water and pass it through the bladder walls to create a negative pressure inside. At the entrance to the bladder is a flap-like hinged door and glands that secrete a sugary mucus that attracts prey.  When the prey brush against small hairs near the trap door, the tension on the door seal breaks and the prey is swept into the trap with a rush of water. Enzymes inside the bladder then digest the food and the bladders establish negative pressure again.

The bright yellow flowers, 1 to 2 cm, are on a stem up to 20 cm long held above the water surface. Each flower has an upper lip, with two lobes, and a lower lip with three lobes.  The floral tube is prolonged into a spur that holds nectar.  The plant is branched in several directions at the base of each flower stalk.  This forms a base that keeps the flower upright.

Plants overwinter by forming winter buds or turions in late summer.  These are masses of tightly compacted leaves that sink to the bottom when the rest of the plant dies in fall. In spring, the winter buds expand, fill with air, rise to the surface and start new plants.

The water crowfoots (Ranunculus flabellaris and R. longirostris) also have finely branched alternate leaves but they lack bladders and bloom in the late spring.  Similar free-floating uncommon bladderworts have flattened alternate leaves (U. intermedia, U. minor), bladders on separate segments from the leaves (U. intermedia), much smaller flowers (U. minor, U. geminiscapa), or whorled leaves and purple flowers (U. purpurea).

  • Links for more info: Sketch of leaves with bladders
  • Origin of the name: Utricularia, L. utriculus, little bottle;  vulgaris, L., common
  • Range:  Across N. America, s. to FL, TX, CA
  • WI Range:  Statewide
  • Common associates: Coontail, milfoil, yellow water lily
  • Wetland Indicator Status: OBL
  • Coefficient of Conservatism: C = 9 (S&W), C = 6 (MI)
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