ZOO TALES: Carnivorous Plants Unique and Evolved
Carnivorous plants have a way of turning the tables on animals. Normally, animals eat plants -- cows graze on grass, giraffes nibble tree leaves, and humans eat all sorts of plants and plant byproducts from apples to zucchini.
But there are types of carnivorous plants that become the eater, rather than the eatee. A plant is considered carnivorous if it attracts, captures, kills and digests animal life forms.
Many plants do some of these things but are not considered carnivorous. For example, many flowers attract birds, insects and a variety of other pollinators. Some plants, such as orchids, jack-in-the-pulpits and waterlilies, temporarily trap insect pollinators to ensure pollen transfer. Still other plants trap and kill insects but do not digest them. Only plants that attract, capture, kill and digest prey are truly carnivorous.
There are about 600 species and subspecies of carnivorous plants, depending on whom you ask, found throughout the world. Like all plants, carnivorous plants must absorb nutrients, either through their roots or leaves. Carnivorous plants get their nutrients from the animals and insects (usually gnats, flies, moths, ants or spiders) they digest. Each genus of carnivorous plant has its own technique to attract and capture its prey. Some have bright colors on the "traps" to attract the prey; others use sweet scents. One species uses suction to pull tiny animals into bladders.
Once they have attracted their prey, some sort of sticky residue, slippery inner stems or some sort of chamber typically hold the captured prey. On some species, downward- pointing hairs and gravity make escape almost impossible.
All carnivorous plants must have sources of enzymes to digest their prey. Some produce the digestive enzymes themselves; others rely on bacteria to produce the appropriate enzymes. The trapped prey simply rots, and the plant absorbs the decomposed molecules.
Most carnivorous plants are found in damp heaths, bogs, swamps, and muddy or sandy shores where water is abundant and where nitrogenous materials are often scarce or unavailable because of acidic or other unfavorable soil conditions.
The largest carnivorous plants, genus Nepenthes (native to the Old World), have large vines that can grow up to 20 yards long and have traps that can hold prey as large as frogs. But for humans and animals larger than a small frog, carnivorous plants are completely harmless. As one expert in carnivorous plants put it, even if you fell comatose onto a bed of carnivorous plants, the worst thing that would happen is that you would smash some lovely plants.
Carnivorous plants are vivid and biologically intriguing, but they are not houseplants. They often need high humidity, high light intensities, acid soil, clean water and seasonal temperature changes -- requirements not normally found indoors.
Two of their greatest threats in the wild are their collection by amateur and professional growers and the destruction of their habitats. Those same wetlands that carnivorous plants need to grow are being drained and are quickly disappearing to development. Many of the species are now either threatened or endangered.
When you find carnivorous plants in the wild, take photographs but, please, leave the plants alone. In North Carolina, one of only two states in which the Venus flytrap grows wild, field collection fines are typically $100-$500 for a first offense and $500-$1,000 for subsequent convictions. Also, for second or subsequent violations, the Plant Conservation Board may levy a civil fine of as much as $2,000.
Visitors to the N.C. Zoo can see three types of carnivorous plants in the park: Venus flytraps (also called Venus' flytraps) and pitcher plants at the Cypress Swamp habitat; pitcher plants at the Mountain Bog, adjacent to the Streamside exhibit; and tropical pitcher plants in the Forest Aviary. Ask a keeper or volunteer to point them out.
Tom Gillespie works for the public affairs office of the N.C. Zoo.
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