Carnivorous plants have captured people's imaginations for centuries, inspiring scientific study, art and literature. Some of the earliest recorded descriptions and illustrations date from the 1200s. Utricularia, commonly called bladderworts, is the most species-rich and widely distributed genus of carnivorous plants. Carl Linnaeus formally described this cosmopolitan genus in 1753; there are over 200 known species.
Utricularia reniformis grows as an epiphyte on tussock grasses in the southern coastal mountains of Brazil, where it may also grows be an epiphyte on other epiphytes, e.g., bromeliads. In cultivation, Utricularia reniformis flowers in spring, together with emergence of the first leaves. These striking lilac flowers are held on a scape up to 60 cm high, above large, fleshy, kidney-shaped leaves. It has thick stolons that carry numerous traps on long stalks. Utricularia reniformis has two types of bladder traps; the genus unlike most other carnivorous genera actively catches its prey.
Charles Darwin is probably the most well known scientist to have studied the elaborate traps of Utricularia. However he was not alone in his fascination; the German scientist Ferdinand Cohn and the American naturalist Mary Treat both studied carnivorous plants during the 1860s and 1870s. Darwin and Treat first corresponded in 1871 and worked collaboratively in their study of the trapping mechanisms of bladderworts. Darwin cited Treat's work throughout his publication Insectivorous plants (1875).
From his observations, Darwin at first believed that prey pushed in the door to Utricularia traps. Initially Treat agreed with Darwin's findings but after further study, she concluded that the prey was drawn into a 'partial vacuum' and that the hairs at the mouth of the trap were sensitive.
The bladderwort trap is indeed active. When set, it is filled with water and a negative pressure is generated on the inside of the trap, making the walls slightly concave. When prey brushes the hairs at the opening, the suction trap is triggered. Water rushes in, flooding the trap and carrying the prey in with it. The mechanism is incredibly fast, with the door opening and closing in less than 1/500 of a second!
Prey size varies according to the species of bladderwort and the size of the traps. Insect larvae, threadworms and other microscopic life have been recorded. Glands on the inside of the trap excrete enzymes that digest prey and absorb nutrients. To set the trap again, water moves from the interior to the exterior via osmosis.
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Taylor, P 1989. The genus Utricularia - a taxonomic monograph. Royal Botanic Garden Kew.