Carnivorous plants

Categories: Angiosperms; Plantae; poisonous, toxic, and invasive plants

Carnivorous plants are a diverse group. All live in nutrient-poor, often boggy or aquatic environments where minerals from digested prey are essential for survival, or at least for good health. None use captured prey as an energy source, as animals do; rather, carnivorous plants are photosynthetic, like other plants. The mechanisms for capturing prey are varied, and carnivory is found in at least nine distinct plant families, having evolved a number of times independently.

Pitchers

One widespread carnivorous mechanism is the formation of pitchers, specialized leaves or portions of leaves that have developed into hollow tubular or pitcherlike structures that contain fluid. The fluid is mostly water but may contain digestive enzymes and mild narcotics. The mouth, or entrance, to the pitcher is generally marked with bright colors and may produce droplets of nectar to attract insects. The throat of the pitcher is usually lined with wax or downward-pointing hairs so that insects will slowly slide downward toward the pool of water but will have great difficulty climbing back out.

Pitchers are found in a number of genera in several unrelated families, though the term "pitcher plant" is most commonly applied to the Sarraceniaceae and Nepenthaceae families, found respectively in the New World and the Old World. Sarracenia is the genus of North American pitcher plants found in bogs, seeps, and marshy areas, primarily in the southeastern United States. The pitchers arise directly from an underground rhizome. A related species, Darlingtonia californica, is found in cold-water bogs in northern California and southern Oregon. The genus Heliamphora includes many species in South America. The Asian pitcher plants are in the unrelated genus Nepenthes. These pitchers hang from the ends of leaves on plants that are generally epiphytic (growing on tree branches) or grow on rocky surfaces. The genus Cephalotus is not related to any of the foregoing but produces pitchers similar to those of Nepenthes. The single species of Cephalotus is found in seeps and bogs in southwestern Australia. Finally, in South America there are species in two genera of bromeliads (pineapple family), Catopsis and Brocchinia, that form crude pitchers that have been found to be carnivorous.

Leaf Traps

The most famous of all carnivorous plants is the Venus flytrap, Dionaea muscipula, which is native to bogs in the coastal plain of North and South Carolina. In this species, the two sides of the leaf snap together quickly when trigger hairs on its surface are brushed twice within a short span of time. The closing mechanism involves a wave of rapid cell elongation on the outer surface of the leaf trap that pushes the two sides of the leaf together. The edges of the trap leaves are lined with long spikes which serve as bars to prevent quick-responding insects from escaping during closing. A reddish coloration and drops of nectar lure insects to the trap. Digestive enzymes are secreted from the inner surface of the trap. After the meal is digested, slower growth of cells on the inner surface reopens the trap.

Related to the fly traps are the sundews, in the genus Drosera, and similar plants in the genera Drosophyllum, Byblis, and Tripohylophylum. Leaves of these plants are covered with tiny glandular hairs, each producing a drop of sticky, nectarlike fluid that attracts the insects and then traps them. Once an animal is tangled in the gluey exudate, digestive enzymes are secreted, and in some, the leaf slowly folds around the prey.

There are many species of sundew, nearly two hundred in Australia alone, with many species in South America, southern Africa, North America, and Europe. The species vary in the size and shape of their leaves and also in their flowers, which come in a variety of colors, sizes, and shapes. They inhabit seeps and bogs or are found in sandy soil that is damp for only a short time. Most of them are tiny rosettes of paddle-shaped to linear leaves, but some are erect, herbaceous tufts 1–2 feet high, or even vines.

One genus of the unrelated family Lentibulariaceae also employs leaf traps. This is Pinguicula, found in North America in moist, nutrient-poor habitats. Its leaves are flat, somewhat curled at the edges, and moderately sticky, without conspicuous glandular hairs. They do not close around prey. The many species of Pinguicula have variously colored, snapdragon-like flowers on long stalks.

Underwater and Underground Traps

The final category of carnivorous plants produces traps under water, or sometimes in damp soil, where they capture tiny crustaceans and other invertebrate animals. Aldrovanda is a submerged plant related to the Venus flytrap but is native to Australia. Its miniature underwater traps snap shut when animals swim or bump into them. Another genus with tiny underwater traps is Utricularia (bladderworts), related to Pinguicula. These traps operate by suddenly expanding to suck water and small animals inside when triggered. The traps are borne on specialized leaves that grow downward into the water or damp soil. Often one only sees the brightly colored, snapdragon-like flowers above the surface. There are hundreds of species of Utricularia, found all over the world, particularly in Australia and North America. A third carnivorous genus in the Lentibulariaceae is Genlisea, which grows in Africa and South America, and which has traps similar to those of Utricularia.

Bibliography

Cheers, Gordon. A Guide to Carnivorous Plants of the World. Angus and Robertson, 1992.

Lowrie, Allen. Carnivorous Plants of Australia. 3 vols. U of Western Australia P, 1987–1998.

Mabey, Richard. The Cabaret of Plants: Forty Thousand Years of Plant Life and the Human Imagination. W. W. Norton, 2016.

Schnell, Donald. Carnivorous Plants of the United States and Canada. John F. Blair, 1976.

Slack, Adrian. Carnivorous Plants. MIT Press, 1980.

Zimmer, Carl. "Carnivorous Plants." National Geographic, March 2010, ngm.nationalgeographic.com/2010/03/carnivorous-plants/zimmer-text. Accessed 20 Feb. 2017.

Carnivorous Plants