- Family: Butterwort Family – Lentibulariaceae
- Growing form: Perennial herb. Rootless, free-floating water plant.
- Height: 20–200 cm (8–80 in.) long. Branched inflorescence 10–25 cm (4–10 in.) high.
- Flower: Corolla Irregular (zygomorphic), dark yellow, sometimes red-streaked, 12–20 mm long, fused, bilabiate, spurred. Upper and lower lip entire, lower lip saddle-like, swelling at base closes corolla tightly, spur descending oblique, 6–9 mm (0.24–0.36 in.) long. Calyx bilabiate. Stamens 2. Gynoecium composed of 2 fused carpels. Inflorescence a 5–10-flowered raceme terminating flowering scape. Often sparsely flowered.
- Leaves: Alternate. Blade narrow-lobed, lobes thread-like, dark green–brown–reddish, lobe tips with different sizes of trap bladder.
- Fruit: Spherical, with glands, irregularly opening capsule.
- Habitat: Inlets and quiet corners in lakes, rivers and brackish springs, ditches, ponds, rivers, excavation sites, reservoirs.
- Flowering time: July–August.
Bladderworts float freely in water or grow as water plants, lying on mud with the water only reaching up to their inflorescence. None of the bladderwort plants have a real root, and they are not usually anchored in the ground. In the absence of a rootstock the job of feeding the plant falls on the leaves. Most bladderworts widen their diet by trapping small insects in its leaf lobes, which have evolved into bladders. Greater bladderwort can have hundreds of these trapped on a single stem. Bladderwort creates a vacuum in its trap bladders by actively pumping the water out of them. Sensitive trigger-hairs arm the trap: the gate in the bladder’s mouth opens inwards and the flow of water sucks prey in in the blink of an eye. Stellate-hairs inside the trap emit digestive substances that make the tissue available to the plant. Bladders are seldom empty, usually there are water fleas, parasitic copepods and the grubs of long-horned flies, but also algae and pollen grains (in average 50%).
Bladderwort’s flower is highly reminiscent of yellow toadflax (Linaria vulgaris), although the plants are not even related. The internal parts of both flowers are however very well protected: yellow toadflax is mainly guarding its store of nectar against insects that are unsuitable for pollination, and bladderwort is protecting its pollen against splashes of water.
The size and appearance of bladderworts can change a lot according to their environment. Depending on how the facts are interpreted, Finland has 5–7 bladderworts, of which 3 are common across the country. Greater bladderwort is most abundant in nutritious waters, even in apparently uninviting dirty ditches and pits. Delicate, light green lesser bladderwort (U. minor) grows mainly in less nutritious waters, small ponds and bog margins. Flatleaf bladderwort (U. intermedia) grows in puddles in bogs and in shallow water in waterside meadows.