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Aquatic bladderworts (Utricularia spp.) are submersed, rootless, carnivorous plants.
Their stems,
with leaflike branching, may grow to over a meter long, and most bear small "urnlike" bladders
that trap and digest tiny animals. These plants also provide habitat for invertebrates and juvenile
fish.
Among Florida's 14 species of bladderwort are two that are often confused because of their similar habit. They have distinctive swollen lateral branches ("floats") that radiate from a node of the flowering stalk like spokes of a wheel.
Both Utricularia inflata and U. radiata form these easily recognized floating "wheels." Both have yellow flowers, and both have submersed stems below the floats with highly dissected leaflike branching. Of course, both have bladders that are typical of the genus. However, upon closer inspection, one can use several other characteristics to distinguish the two species.
The larger of the two is U. inflata, with usually longer, wider floats and a flower scape rising as much as 15 cm above them (compared to a maximum scape length above the floats of 6 cm for U. radiata). Also, the floats in U. inflata gradually taper in width toward the center of the whorl, while those in U. radiata do not, except for a brief, more abrupt tapering near the axis. But admittedly, such morphological features can be difficult to discern when you have only one of the two species at hand.
Clearer distinctions can be found in the inflorescence. The scape of U. inflata may bear 4 to 18 flowers, with a usual number of 10 or 11, while U. radiata may bear 1 to 7 flowers but most often has 3 or 4. The individual mature fruiting stalks are usually recurved (bent downward) in U. inflata, and nearly always erect or ascending in U. radiata. The small leaflike bract at the base of individual flower stalks is definitely longer than broad in U. inflata, and unlobed; in U. radiata, the bract is lobed and broader than long. And not least of all, the protrusion of extra petal tissue seen on the "back" of each flower i.e., the corolla spur differs in the two plants: its tip is usually notched in U. inflata, and not so in U. radiata.
The two species also differ in their mode of vegetative reproduction. When plants of U. inflata are stranded on exposed muck or mud, they frequently produce long threadlike branches among the "leafy" stems, with each "thread" bearing a tiny tuber at its tip. U. radiata does not produce tubers, but under similar conditions will form tiny vegetative buds at the axils of smaller branches. (Either species may turn up in great numbers following a drought or drawdown event in a shallow waterbody, and then return to relative obscurity in the plant community at higher, stabilized water levels.)
Both of these bladderworts occur in all regions of the state, although U. inflata is the more commonly seen species. Its distribution extends on the Coastal Plain from New Jersey and Delaware to south Florida, and west to eastern Texas. The smaller species, U. radiata, is more cold-hardy, and ranges north to Nova Scotia, west to Indiana and Arkansas, and south to Florida.
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