Stems: immersed, scape stout, naked, three to four inches high, with a few scales. Leaves: two to three pinnately many-parted, capillary, bearing many bladders. Flowers: three to twenty in a raceme on short pedicels, the sides of the lips reflexed, spur conical, slender, rather acute. Fruit: capsule many seeded.
The Greater Bladderwort is a very curious plant which grows in shallow pools and ponds, and has yellow flowers similar in structure to those of the Butterwort. The leaves, usually much crowded on the floating branches, are divided into thread-like segments bearing the numerous, velvety-looking, little air bladders. In the autumn, buds terminating the stems fall off, and are buried in the mud at the bottom of pools until springtime, when they root, and the new bladders, at first filled with water, soon fill with air, and the plant, leaving the mud, rises to the surface of the pool and flowers, the bladders feeding it by means of their trapping. The pale green bladders are, however, its most interesting feature, for having no roots the plant floats submerged by means of these tiny inflated balloons, whose bristle-like appendages give them the appearance of crustaceans. These bladders have an opening closed by a valve and furnished with a few projecting bristles that guide insects to the aperture, which they enter by pressing against the lid. Inside the bladder is covered with glandular processes that seem to absorb the fluid products of decay, but do not, like the Butterwort and Sundew, digest the trapped victim and absorb the animal matter. The yellow flowers grow in racemes of three to twenty at the top of the stalks on pedicels which are recurved in fruit. They have a two-lipped corolla with an erect, entire upper lip, and a broad three-lobed lower lip that has a large palate, and a conic spur nearly as long as the lip to which it is appressed.
Utricidaria intermedia, or Yellow Bladderwort, has also a naked scape bearing one to five yellow flowers, the upper lip of whose corolla is much longer than the palate, the acute spur being appressed to, and as long as the very broad lower lip. The slender pedicels are erect in fruit. The branches are floating, and the leaves more or less scattered, with linear, flat segments and bristle-toothed margins. The bladders are, with rare exceptions, borne on leafless branches.