Utricularia

Bladderworts, known scientifically as *Utricularia*, are a group of roughly 233 species of carnivorous plants (some classifications put the number at 215, as in a 2001 study). They grow in freshwater or wet soil, either rooted in the ground or floating in water, and can be found on every continent except Antarctica. Enthusiasts cultivate them for their flowers, which are often likened to those of snapdragons or orchids.

Every species of bladderwort is carnivorous, using tiny bladder-like traps to catch small organisms. Terrestrial types have very small traps that feed on microscopic prey like protozoa and rotifers in waterlogged soil. These traps range from 0.02 to 1.2 cm (0.008 to 0.5 in) across. Aquatic species, such as the common bladderwort (*U. vulgaris*), have larger bladders that can capture bigger prey, including water fleas (*Daphnia*), nematodes, mosquito larvae, young tadpoles, and even fish fry. Despite their size, the traps are highly sophisticated. In aquatic species, the trap is set under negative pressure. When prey touches trigger hairs near the trapdoor, the door opens and the prey, along with surrounding water, is sucked inside. The door then closes, the whole process taking just ten to fifteen milliseconds.

Bladderworts are unusual plants with a highly specialized structure. Unlike most flowering plants, they lack a clear separation into roots, leaves, and stems, and they have no root system at all. Their bladder traps are considered one of the most complex structures in the plant kingdom.

The main part of a bladderwort plant always lies beneath the surface of its substrate. Terrestrial species sometimes send up a few photosynthetic leaf-shoots, while aquatic species can be seen below the surface of ponds and streams. Most species produce long, thin, sometimes branching stems or stolons under the surface, whether in pond water or in dripping moss in a tropical rainforest canopy. Both the bladder traps and photosynthetic shoots are attached to these stolons. In terrestrial species, the shoots push upward through the soil into the air or along the ground. The name "bladderwort" comes from these bladder-like traps. Early observers thought the bladders of aquatic species were flotation devices before discovering they were carnivorous.

The genus name *Utricularia* comes from the Latin *utriculus*, a word that can mean wine flask, leather bottle, or bagpipe.

Flowers are the only part of the plant that rises above the soil or water. They grow at the end of thin, often vertical stalks and range from 0.2 to 10 cm (0.08 to 4 in) wide. Each flower has two unequal, lip-like petals, with the lower one usually much larger than the upper. They can be any color or combination of colors, and their structure is similar to that of the related carnivorous genus *Pinguicula*. The flowers of aquatic species like *U. vulgaris* are often described as small yellow snapdragons, while the Australian species *U. dichotoma* can look like a field of violets on nodding stems. The epiphytic species from South America are generally considered to have the showiest and largest flowers, and are frequently compared to orchids.

At certain times, a plant may produce closed, self-pollinating (cleistogamous) flowers, while at other times or in other places the same species may produce open, insect-pollinated flowers, with no clear pattern. Sometimes individual plants have both types at once. For example, aquatic species such as *U. dimorphantha* and *U. geminiscapa* usually have open flowers above the water and one or more closed, self-pollinating flowers below it. Seeds are numerous and small, ranging from 0.2 to 1 mm (0.008 to 0.04 in) long for most species.

Bladderworts can survive almost anywhere with fresh water for at least part of the year, except Antarctica and some oceanic islands. The greatest species diversity is in South America, with Australia close behind. Like most carnivorous plants, they grow in moist, mineral-poor soils, where their carnivory gives them an advantage. Terrestrial bladderworts often grow alongside other carnivorous genera like *Sarracenia* and *Drosera* in very wet areas where moving water removes soluble minerals from the soil. The genus includes terrestrial, lithophytic, aquatic, epiphytic, and rheophytic forms, all highly adapted to their environments. About 80% of species are terrestrial, mostly in waterlogged or wet soils where their tiny bladders are constantly exposed to water in the substrate. They are often found in marshy areas with a high water table. Most terrestrial species are tropical, though they occur worldwide. Around 20% of species are aquatic. Most of these drift freely on the surface of ponds and other still, muddy-bottomed waters, only rising above the surface to flower. A few are lithophytic, adapted to fast-moving streams or even waterfalls. They are usually found in acidic waters but can grow in other conditions.