Insectivorous Plants

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Introduction

Insectivorous Plants, also carnivorous plants, plants that gain some of their nutrition from animals, especially insects, captured by the plants themselves. Most occur in bogs where the soil is acid and poor in available nitrogen; capturing insects is one way of getting nitrogenous compounds without manufacturing them. At the same time, the green leaves of these plants manufacture carbohydrates. The trapping mechanism of insectivorous plants is relatively small. Therefore, prey is almost inevitably limited to small insects.

Insectivorous plants are diverse and represent members of three orders of dicots: Nepenthales, Scrophulariales, and Rosales. A majority are in the Nepenthales, including the pitcher plant, sundews and the Venus's-flytrap, and East Indian pitcher plants. Others include the bladderworts, butterworts, and the Australian pitcher plant. Discussed below are the sundews and bladderworts. Certain species of fungus are known to be carnivorous as well.

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Sundews

The sundews include about 90 to 100 species of mainly perennial herbs. Found worldwide, they are among the most common of insectivorous plants. The small white, pink, or purple flowers grow alone or in one-sided clusters. The leaves form small rosettes on the ground in bog areas; the upper surface of each leaf is covered with prominent, gland-tipped, green to reddish hairs. The glands excrete a clear, sticky fluid that clings to them like dewdrops; the name sundew is taken from these drops, as they are not dried up by the sunlight. If a small insect alights on the leaf or brushes past it, it is held fast by the sticky hairs, which curve inward and press the victim down onto the surface of the blade, where it is digested.

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Bladderworts

The bladderworts make up about five genera of widely distributed herbs. The most widespread genus contains about 275 species found in temperate and tropical regions throughout the world. Some species of this genus are aquatic and others terrestrial. Several tropical species are air plants (see Epiphyte) resembling orchids. Among the aquatic bladderworts, some root in the mud; others, such as the common bladderwort, are rootless, floating freely in ponds. The common and scientific names of the genus refer to the many utricles, or bladders, borne on the leaves of the common bladderwort.

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The bladders of the common bladderwort range up to 0.5 cm (up to 0.2 in) in diameter. Each has an orifice that is guarded by bristles. When tiny aquatic insects or other animals, including minute fish, touch these bristles, the bladder suddenly dilates, sucking in and trapping the animal. By digesting its prey, the bladderwort obtains the food that plants normally get through a root system.

Other family members include the purple bladderwort, common in eastern U.S. ponds, and the nonaquatic butterworts.

Scientific classification: The Australian pitcher plant belongs to the family Cephalotaceae and is classified as Cephalotus follicularis. Sundews make up the family Droseraceae. Bladderworts belong to the family Lentibulariaceae. The most widespread genus of bladderworts is Utricularia. The common bladderwort is classified as Utricularia vulgaris.

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