Swollen Bladderwort, Utricularia inflata

Tuesday, August 11, 2009

Nature Notes
by Bob Thomas

Some plants just catch your attention. Such is the case with the swollen bladderwort (Utricularia inflata), Family Lentibulariaceae. It is a denizen of clear freshwater wetlands, but can survive in muddy situations if the water dries. Swollen bladderworts are native to the southeastern United States, but have been introduced to other parts of the United States where they are considered to be invasive species.

These insectivorous plants are virtually invisible to the untrained eye. The vegetative growth is entirely submerged and is a perennial that can become extremely dense, often resembling a thick hair-like mat just under the surface. They have no leaves, but do have filamentous branches off the growing stolons that are the main growth structures. Some botanists argue that these filaments are indeed leaves. Bladderwort do not have extensive root systems, but they may be somewhat loosely anchored.

Bladderworts capture their tiny invertebrates in the near spherical, one to three millimeter-long traps, or bladders (hence the name, bladder [traps] and wort [Middle English word for plant]). The traps are located in the axils of the branches. When prey touch the bladders, a trap door is sprung creating a vacuum that sucks the prey into the bladder.

Enzymes produced by the plant then digest the prey item. The most obvious part of bladderwort is the unique floral component. An inflorescence of up to 20 yellow flowers sits at the end of a stalk that extends about five inches above the water's surface.

When bladderwort is in full flower, one sees small yellow flowers randomly sticking out of the water, usually mixed with other aquatic species like water-shield (Brasenia schreberi) and fragrant water lily (Nymphaea odorata). Close inspection reveals that the flower stalks are supported by what is called a float consisting of four to 10 spongy spokes radiating from the base of the stalk. Each spoke of the float is branched and has bladders in and among the branches. The float with its flower develops underwater, and as the flower prepares to open, the float begins its ascent to the surface of the water. The flowers often open underwater and then emerge in full glory.

Reproduction is by seed production and asexually by fragmentation of the vegetative portion of the plant. When their habitat dries, they may produce small tubers that allow them to survive until the water returns. Some say aquatic birds playing Johnny Appleseed with vegetative fragments often spread it.
The bottom line is that this is one neat plant species that needs to be on your naturalist target list.

                                        

Vegetative growth of swollen bladderwort,                                    Vegetative growth of swollen bladderwort
Utricularia inflata, under water. Note the                                       showing the tiny insectivorous bladders
fragrant water lilies (large leaves) and                                          (traps).
water-shield (oval leaves). All photos taken                                   Photo by Bob Thomas.
at Paul B. Johnson State Park, Hattiesburg,
Miss.
Photo by Bob Thomas.

                                       

Flower and "float" of swollen bladderwort                                     A similar photo.
adjacent to fragrant water lily leaves.                                          Photo by Bob Thomas.
Photo by Aimee Lee.