Bladderwort (Utricularia spp.)
Updated: Oct 5, 2020
Bladderwort is one of the most common aquatic plants in Conway Lake and is easily identified by the small bladders (2-4 mm in diameter) on its branched leaves. The plant is typically loosely anchored to the bottom and can grow to heights of 2-3 feet. You may also see it detached as free-floating mats.
Four different species of bladderwort have been identified in Conway Lake:
Purple bladderwort (Utricularia purpurea) - The bladders are located at the tips of the leafy branches. Very common in Conway Lake.
Common bladderwort (Utricularia vulgaris) - The central stalk often zig-zags between alternating branches of leaves. Each branch is forked a few to several times into thread-like segments. Small reddish bladders extend from leaf filament axils. Common in Conway Lake.
Flat-leaf bladderwort (Utricularia intermedia) - Leaves are elliptic to nearly round in outline, divided near the base into 2 or 3 main divisions, and the primary divisions each forked 2 to 5 times. Small bladders for capturing micro-organisms are present on specialized, leafless stems.
Floating bladderwort (Utricularia radiata) - There are two quite different types of leaves. The lower leaves are alternate, up to 3 cm long, and divided many times into hair-like segments, each bearing many tiny bladders. The upper leaves immediately below the flowering stem are in whorls of 4-7, 1-4 cm long, and are inflated, serving as "floats" so that they ride on the water surface.
Bladderwort Species Comparison Chart (source: Maine Field Guide to Invasive Aquatic Plants and their common native look alikes, p. 68)
Interesting Fact: bladderwort is a carnivorous plant feeding on small insects, larvae and other planktonic organisms. The bladders are not little floats – they are for capturing prey. There are trigger hairs on each bladder that open a trap-door and suck in water along with the organism that triggered the reaction. Once inside the bladders, the organism is digested by enzymes, then special cells take the digested material and move it to the stem. See photo at bottom of page.
Look Alikes: Bladderwort may resemble the milfoils, but there are two key distinguishing features. One is the bladders on the leaves for which the plant is named. The other is that milfoils have feather-like leaves that have one central leaf stem with nearly opposite unbranched leaflets. The leaflets of bladderwort are more of a branching-forking configuration.
Purple bladderwort (Utricularia purpurea) - photographed in Dolloff Cove by Don Yurewicz
Common bladderwort (Utricularia vulgaris) on the left, and flat-leaf bladderwort (Utricularia intermedia) on the right. Common bladderwort has coarse, alternately arranged branch-divided leaves whereas flat-leaf bladderworts have slender stems with numerous, crowded, finely dissected leaves. Collected in South Cove by Maria Gross.
Floating bladderwort (Utricularia radiata) showing the upper floating leaves (bottom of photo) that are inflated and serve as floats, and the lower leaves with small bladders typical of bladderwort (upper part of photo). Photo by Maria Gross
Microscopic view of the bladders on a bladderwort. (http://www.lakestewardsofmaine.org/mciap/herbarium/Bladderworts.php)