Timothy J. Malinich teaches and writes on many topics including nursery and greenhouse production, propagation and pesticide safety. He has worked in the horticulture industry for over 40 years.

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“Man Eating” Plants
by Timothy J. Malinich    

You don’t need to watch a sci-fi horror flick to hear tales of vicious monsters or man-eating plants. These already exist in the forest and landscape … and can give you a taste of just how nasty nature can be. 

As the name implies, carnivorous plants eat flesh. They feed for the same reason that we do: nutrients. Plants need nutrients and carnivorous plants typically grow in nutrient-poor areas. In order to survive, they have developed intriguing means of luring, trapping, and digesting prey. They have filled a niche that allows them to grow and reproduce in areas where other plants find it difficult to survive. These plants survive in bogs, fens, and waterways. They prefer full sun and do not compete well with surrounding vegetation. All of the U.S. species and most of the non-domestic species prefer acidic soils or substrates and all require moist conditions. 

Pit traps are a passive and very successful means of collecting food. Pitcher plants (Sarraceniaspp.) are long-lived rhizomatous perennials and some form clumps of traps. Some are short (under 1 foot), such as purple pitcher plant (S. purpurea). S. flava, on the other hand, are tall (1-2 feet), graceful, and can be found in shades of greens, purples, and white. Both flower annually on tall flower stalks well above the pitchers (no sense eating the pollinators they depend on).

The trap consists of several precise constructs. A leaf-like lid, or umbrella, is suspended over the trap opening. Those of S. purpureaare upright and open to rainfall; on S. flavaand others, the lid is more umbrella-like, protecting but not restricting the opening. The lid and lip of the trap are brightly colored to attract prey. The lip (or perhaps tongue?) is a small outward roll of leaf at the top edge of the pit that provides a comfortable landing area. Below the landing pad is a smooth waxy tube that few insects could climb and rows of downward-pointing hairs. All along that slippery tube and just out of reach of the prey is an area full of nectaries promising sweet droplets of food to any insect that makes it that far.

As the insect reaches for the nectar, it is unable to reverse direction due to the hairs and cannot gain a foothold on the waxy tube. It falls down the tube into a pool of digestive fluid where it is broken down and absorbed by the plant. You can feed these open-topped plants – it’s quite satisfying to pick a Japanese beetle from your favorite rose and drop it into aSarraceniatrap! At the end of the season, you can even dissect a pitcher plant and see the skeletal remains of its victims.

A variation of the pit trap is seen on cobra plants (Darlingtonia californica). This trap is almost totally enclosed with a hood, the “head” of the “cobra.” The landing pad is a tongue extending from the bottom of the hood. The insect lands on the attractive tongue and walks into the hood where translucent areas around the top confuse the insect, which tries to fly toward the sun though it cannot escape that way. Eventually the trapped insect falls into the digestive liquid in the bottom.

Sticky traps actively capture their prey. Sundews (Droseraspp.) are tiny plants, many no larger than a quarter. Their leaves are covered with tentacles, each sporting a drop of sticky mucilage at the tip. Attracted by the glistening liquid or bright red color, tiny insects are easily caught by the tentacles. Then the horror begins. The long tentacle holding the prey bends inward; nearby tentacles join in, trapping and suffocating the hapless quarry. The sticky mess is pulled to the center of the leaf where digestive fluid is added to the mix. The prey is digested, and the nutrients absorbed by the leaf.

This slow mechanism is powered by growth of the tentacles. The insect stimulates release of a growth hormone, causing the directional growth of the tentacle stalk; the process can take 20 minutes or longer. If you have ever used a weed killer on your lawn, you have seen something similar as the weeds curl within hours of the application.

Smaller Droseraspecies form mats of many tiny plants. The tall threadleaf sundew (D. filiformis) will grow linear glistening leaves over 6 inches tall. A sundew relative, dewey pine (Drosophyllum lusitanicum), is a Mediterranean plant and actually prefers drier conditions than the typical carnivorous plant.

Butterworts (Pinguiculaspp.) rely on flypaper-like leaves to capture and hold their meals. The leaves of these small flat plants (2-3 inches) emit an earthy odor to attract small gnats and flies. After landing on the leaves, the insects are stuck to mucilage secreted from glands on the leaf. As with Drosera, the insect is then digested and its vital nutrients absorbed.

The poster child of the carnivorous plant world is the Venus flytrap (Dionaea muscipula). Its leg-hold style trap is fast enough to catch most flies or ants that venture inside and the trap is large enough for everyone to enjoy the show. Two lobes joined at their base by a ridge of cells capable of reacting to a small electrical impulse make this trap deadly. And if you really think of it, the mechanism found in this plant is amazing.

Each half trap has three trigger hairs. Two hairs must be tripped in less than one minute, or one hair touched two times within the same time limit. This trigger sends a small electrical impulse to the hinge of the trap. This hinge holds the trap open by regulating the water and chemical balance in the hinge – an effort that costs the plant energy. When it receives the electrical impulse, the hinge releases and the trap quickly close, but not all the way. The teeth at the edge of the trap hold the prey until a much slower growth response fully closes and seals the trap. If you examine a closed trap you will often see a leg or antenna reaching through the teeth, in vain, for freedom.

You may not find carnivorous plants in your garden, but you can see them in conservatories, private collections, and garden centers. Many states have native populations of carnivorous plants … there just might be some in your local park. The world is full of wild, wonderful, and terrifying lifeforms. 




This article appeared in a previous State-by-State Gardening publication.


Posted: 06/24/19   RSS | Print


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