Take a fascinating botanical journey beyond garden favorites such as the tulip, lily or pansy and into the realm of weirdly wonderful carnivorous plants. In this excerpt from Bizarre Botanicals (Timber Press, 2010), authors Larry Mellichamp and Paula Gross offer tips and tricks on how to grow your own carnivorous plants at home and how to and observe their digestive mysteries.
If one group of plants is across-the-board weird and fascinating to the greatest variety of humans—young and old, plant-loving and plant-indifferent—surely it is the carnivorous plants, which “feed” on flesh. Widely grown, often misunderstood, they seem to defy explanation.
Why are they so universally intriguing? Because their lifestyles violate what seems like a fundamental rule of life on earth: plants don’t eat meat—in fact, they don’t eat at all! They make their own food and form the base of the food web. Everything else eats plants (or other creatures which themselves eat plants). A plant is for food and making oxygen, for creating habitats and providing fuel, fiber, and spices. Even if we don’t often consider those “nurturing” qualities of plants, we at the very least think of plants as passive scenery. Carnivorous plant behavior is so fundamentally unplantlike, it flies in the face of reason (pun intended). No one expects a plant to turn the tables and actually capture and kill the insects that come seeking to graze upon its green bounty. A plant grabbing a bug and eating it? Agh! What’s next? If a plant can eat a fly, maybe there is a plant out there that could eat me. Our imaginations run wild from there.
Even rational scientists with their fantasies in check are captivated by these amazing plants. Charles Darwin considered carnivorous plants fascinating, especially sundews and Venus flytraps, and studied them much of his life. In his 1875 book Insectivorous Plants, the first treatise devoted to these plants, he reported his detailed experiments on their movements in capturing and digesting prey. He found, for example, that a pebble would cause a flytrap to close but not seal tightly, and the plant would simply reopen the next day. Add some protein, however, like egg albumen, and this would trigger the tightening of the trap and the release of digestive enzymes. The plant could tell when it had caught a real meal.
So why does a plant that can make its own food by photosynthesis need to eat meat? The short answer is, to supplement its nutritional needs and allow it to compete and grow in nutrient-poor habitats. The next logical question is, “How does it manage to eat?” (with no teeth, stomach, or intestines). Before we reveal those secrets, let’s take a quick look at who makes up this rogue’s gallery of plants with a taste for prey.
More than 600 species of carnivorous plants have been recognized in the world, yet most of them can be divided into basically five different types—pitcher plants, sundews, butterworts, bladderworts, and the one and only Venus flytrap. Pitcher plants are the largest carnivorous plants and have tubular leaves that form pitfall traps. Sundews have variously shaped leaves that are absolutely covered in glistening, sticky hairs that act like flypaper, engulfing small insects in a mucilaginous mire. Butterworts have rosettes of broad, slimy leaves for insects to stick to. Bladderworts grow in water or waterlogged soil and bear many tiny, bladder-shaped leaves that quickly inflate to suck in miniscule prey. Because these leaves are so small and grow underwater or in the soil, they are not easily observed, and we do not cover them in this book. Last but not least is the international poster child for carnivorous plants, the Venus flytrap. Only one species is recognized from one area of the world, the coastal Carolinas. Its rapid-action and bear-trap-type leaves seem the ultimate in plant-turned-predator innovations.
Suppose a mild-mannered plant wanted to join this gang of insect-eaters. What does it take to earn the title of carnivorous plant? The “How to Be a Carnivorous Plant in Four Easy Steps” mantra sounds something like this: Attract. Capture. Digest. Absorb.
Western Australian Pitcher Plant
Plant type: Herbaceous perennial
Height and spread: Clumps 2 in. × 3 in. (5 cm × 8 cm)
Growing Tips
Difficulty rating: 3
Indoors vs. outdoors: Indoors with humidity and temperature controls
Light: Bright light
Hardiness: Not hardy
Moisture: Keep constantly moist but not sopping wet
Growing medium: 50% peat, 30% sand, 20% perlite
Notes: Barely tolerates night temperatures above 70°F (21°C)
We are not generally drawn to carnivorous plants because they are cute. But Cephalotus follicularis, the smallest of the true pitcher plants, is just that to some observers. Like a Chihuahua with an inner rottweiler, it is adorably miniature on the outside but vicious if you get too close.
This is the one species in the genus, and it occurs only in a narrow area of southwestern Australia from Augusta to Cape Rich. There it grows mainly in open, sunny, marshlike wetlands in acidic, sandy soils and on seepage cliffs. When I first saw this plant, I was hiking down a steep slope along an ocean inlet where the cliffs are partly formed from seams of coal, called Coalmine Beach. I gasped upon seeing it on the cliffs, as I had come so far for this very purpose. I was transfixed, looking at an array of 6 in. (15 cm) diameter clumps of perfectly formed, hairy, bloodred pitchers, each 3/4–2 in. (2–5 cm) tall.
Like almost all pitcher plants, the open mouth of the pitcher leaf is partially covered by a hood, which keeps out most rainfall (so as not to dilute the digestive enzymes). These hoods appear almost striped, with translucent sections alternating with dark red sections. The most gruesome features of the pitchers are their teeth, which incurve like fangs over the rim of the pitcher mouth. You can get a cheap thrill by carefully inserting your finger into a Cephalotus pitcher. As you try to withdraw it, the plant’s fangs will grip on, kind of like a botanical Chinese finger trap. These diminutive pitchers are remarkably tough in texture, and you can actually end up with a sore finger! Each pitcher has prominent hair-edged wings on its front exterior that may serve as a sort of ladder by which insects may crawl up to their doom.
The western Australian pitcher plant is among the most difficult carnivorous plants to grow well in cultivation, perhaps because it requires somewhat paradoxical conditions—a combination of very moist yet well-aerated soil; pure water and high humidity, but with air movement; and lots of sun, but not consistently high temperatures. If you would like to try your hand, purchase it from reputable dealers who can give you advice on growing these cute little killers.
Did You Know? You can get a cheap thrill by carefully inserting your finger into a Cephalotus pitcher. As you try to withdraw it, the plant’s fangs will grip on, kind of like a botanical Chinese finger trap.
Venus Flytrap
Plant type: Herbaceous perennial
Height and spread: 3 in. × 3 in. (8 cm × 8 cm)
Growing Tips
Difficulty rating: 2
Indoors vs. outdoors: Outdoors. North of zone 7, bring indoors for winter just before first frost
Light: Full sun
Hardiness: Zone 7
Moisture: Keep constantly moist but not sopping wet
Growing medium: 60% peat, 40% sand or perlite
Notes: Best grown as part of a larger bog dish garden with other small carnivorous plants. Do not grow in enclosed terrarium in full sun
Oh yes, the weirdest of the weird, the pinnacle of carnivorous plantdom, the most famous plant in the world. How did this single species of a plant, no bigger than your hand and growing only in coastal wetlands of the eastern Carolinas, make it to worldwide stardom? Flashy character? Devious behavior? Great management and representation? Well, the flytrap has had its influential promoters—John Bartram, Thomas Jefferson, and Charles Darwin, who wrote of it in Insectivorous Plants and referred to it as “one of the most wonderful plants in the world.” But unlike many rock stars today, the Venus flytrap doesn’t need a lot of hype to draw attention. This star has made the world scene due to its own natural talents: colorful leaves that act like a bear trap, dramatic spines that look like gruesome fangs, split-second movements made in response to visiting insects, transformation into a green “stomach” complete with digestive juices that sometimes ooze from its margins. All Dionaea muscipula ever needed was a catchy common name.
Kids rarely fear the pitcher plants or sundews in the bog plant displays at our university botanical gardens, but the Venus flytraps elicit a fear-excitement response. “Will it hurt if I put my finger in it?” “If I left it in there, would it dissolve my finger?” “How big do they get?” With this last question you can see their imaginations growing, and their hopes that maybe their pesky little brother might stumble into such a giant trap. Sometimes there is a little disappointment when they learn that the only creatures in danger are insects. But this does not last long, and most are eager to buy one and take it home for close observation.
The Venus flytrap grows as small rosettes or clumps of leaves (the stems are bulblike rhizomes underground). The actual traps are rarely more than an inch long, often with red coloration. Along the lobe margins are soft “teeth” that give the trap an extra margin of reach to ensnare those quick insects with hair-trigger reflexes for escape. On the inside of each trap lobe are three actual “trigger hairs,” several millimeters long, that must be touched twice within twenty seconds (or two hairs touched) in order for the trap to snap shut in less than a second. This assures that nonliving disturbances do not cause the trap to close, expend energy, and get cheated out of a meal. If you make the traps close without feeding, they will reopen within twenty-four hours but are worse for the wear.
This gets at the mechanism of trap closure. Many scientists believe the closure action is caused by extremely rapid growth, where the cell walls suddenly soften and intracellular pressure causes the cells to grow faster on one side only, such that the leaf very rapidly “grows” itself shut. Then it must grow itself open, but this happens slowly over the course of a day. They can do this only so many times before they wear themselves out and no longer function. Once Venus flytraps detect prey, they close so tightly that the trap becomes convex, forming a sort of stomach around the victim, to the point that it secretes digestive juices and can appear to actually drool. Mmm.
After four to ten days, depending on the size of the prey, the trap reopens and the undigested husk of the insect lies crumbled against the wall of the trap. If a trap catches a particularly large insect, extra digestive juices may be secreted such that the trap leaves themselves are damaged and turn black. Similarly, if a trap is fed something rich in protein, like hamburger, it can die. To avoid this “indigestion,” only feed your flytraps freshly killed insects or small arthropods such as spiders, centipedes, and pill bugs.
Literally millions of Venus flytraps are grown every year from tissue culture and seeds to satisfy public demand. What kid (and often adult) has not tried to grow one? Yet many have not seen them live very long. It is not that they are especially difficult, but they do have some absolute requirements, and growing inside as a houseplant is not one of them. They must be grown in full sun, in an acidic medium, and kept always moist. Cultivation practices are based on mimicking the plant’s natural habitat—that of the wet, low-nutrient pine savannas and bogs within a 60-mile radius of Wilmington, North Carolina. Historically the Venus flytrap had a slightly larger range, but it has been restricted by habitat loss due to drainage and development. Its natural habitat is fragile and dependent on constant moisture and frequent fires to burn off overgrowing vegetation. In the past, flytrap populations may have suffered from overcollecting. Currently U.S. law protects the plants in the wild, with collection punishable by fines of up to a thousand dollars per plant. Ironically, habitat can be drained and thousands of plants killed without any fines at all. But we do treat our stars, however much esteemed, paradoxically sometimes. Highly valued yet pushed to give us more, and sometimes the pressure is just too much. I hope the fascination and wonder inspired by growing the Venus flytrap will lead to greater curiosity about the universe of plants, weird and familiar alike, and bring renewed concern for preservation of wild species amidst our practice of wanton habitat destruction.
Did You Know? Once Venus flytraps detect prey, they close so tightly that the trap becomes convex, forming a sort of stomach around the victim, to the point that it secretes digestive juices and can appear to actually drool.
Marsh Pitcher Plant
Plant type: Herbaceous perennial
Other common name: South American pitcher plant
Height and spread: Clumps 6 in. × 6 in. (15 cm × 15 cm)
Growing Tips
Difficulty rating: 3
Indoors vs. outdoors: Indoors with humidity and temperature controls
Light: Bright light
Hardiness: Not hardy
Moisture: Use pure (unchlorinated) water to keep moist but not wet. Likes high humidity
Growing medium: 50% peat, 50% perlite
Notes: Barely tolerates night temperatures above 70°F (21°C)
In the 1840s the first European explorers finally reached the remote, flat-topped sandstone mountain formations called tepuis in the Guiana Highlands of southern Venezuela. These scattered, mesa-like formations can rise to 3000 ft. (914 m) or more above the surrounding territory, and are effectively like islands. Such habitat isolation usually brings about the existence of many endemic plants and animals—creatures found only from those single, isolated locations. The mist-shrouded tepuis are home to many such endemic plants, and some of the first to be collected by European explorers were the Heliamphora pitcher plants. Since that time at least fourteen species have been described, with the anticipation of more to be found on yet unexplored tepuis. How they arrived, how they are related to Sarracenia of North America, and how they evolved on these high-altitude, cold-but-sunny, rocky, treeless, rain-drenched, marshy savannas, no one knows. They are cloaked in mist and mystery.
Most heliamphoras have particularly handsome, elegant, and well-proportioned forms. The graceful lines of the pitchers, the curve of their openings, and their coloration are reminiscent of beautiful blown-glass sculpture. Their hoods are greatly reduced into little, cupped, knoblike structures called nectar spoons. These are often red and secrete nectar, attracting prey. The pitchers have wide, sloping openings to admit insects, and many downward-pointing hairs to prevent escape. As the hoods are not large enough to keep out rainwater, many species have a special notch partway down their pitchers. This serves as a sort of overflow valve to drain excess water out of the pitcher before it spills over the top, carrying the nutritious insect juices with it. These species do not produce their own digestive enzymes, relying instead on the fungal and bacterial soup effect to decompose prey and make available extra nitrogen and other nutrients. The high rainfall of the area leaches nutrients from the thin soil. The ability to derive extra minerals from animal prey gives heliamphoras and the sundew species that grow there a survival advantage.
Heliamphora (like Darlingtonia and Cephalotus) is not easy to grow in cultivation, requiring those elusive cooler nighttime temperatures, bright light, high humidity, and yep, you guessed it, always moist, but well-aerated, freely draining soil. Heliamphoras are less readily available than most other carnivorous plants, so you will need to search a little harder to acquire one. But then, so did (and still do) the botanical explorers of the mist-shrouded tepuis of the Guiana Highlands. The fastest way to get there these days is by helicopter—or if you prefer, a three-day overland hike and then up a 3000 ft. (914 m) vertical cliff!
Butterwort
Plant type: Herbaceous perennial
Height and spread: Flattened rosette to 2 in. × 3 in. (5 cm × 8 cm)
Growing Tips
Difficulty rating: 2
Indoors vs. outdoors: Outdoors. North of zone 7, bring hardy species indoors for winter just before first frost. Tropicals never below 40°F (4°C)
Light: Bright light
Hardiness: Zone 7
Moisture: Keep constantly moist but not sopping wet. Prefers slightly higher than average humidity
Growing medium: 50% peat, 50% sand or perlite
How does an insect-digesting plant get a common name like butterwort? Respected authors seem to disagree on the meaning of the names. Pinguicula is the genus. The Latin pinguis means “fat,” or some have translated it into “little greasy one”—not a strict reference to butter, though. The common name of butterwort may have arisen on its own, simply from the appearance of the leaves of European species. German monk and botanist Vitus Auslasser referred to the plant as Zitroch chrawt, roughly meaning “lard-herb.” The leaves do look a bit like slices cut from something smooth and greasy, like lard or butter. What looks like grease from a distance is actually sticky mucilage, produced on small hairs covering the surface of the pale green leaves. The true nature of these hairs is revealed when you see flies (usually gnats) in the butter.
About eighty species of Pinguicula are scattered across the globe, in both temperate and tropical regions. While their seasonal behavior and appearances may vary, they all exhibit similar forms and flower structures. Butterworts are low-growing, rosette-forming plants usually measuring 1–7 in. (2.5–18 cm) in diameter. At certain times of year the rosettes produce showy flowers on tall stalks that greatly exceed the height of the sticky leaves. These are almost always pleasingly asymmetric in form (much like the flowers of violets) with long nectar spurs and variously colored petals of purple, pink, yellow, or white, depending on the species. But the carnivorous action happens on the leaves, of course. What seems merely greasy to our touch is actually quite sticky to small insects landing on the glistening leaf surfaces. Butterwort leaves respond to the presence of prey by secreting more mucilage, with which they further ensnare their victims. It has been shown (through radioactive tracing) that nitrogenous compounds from insects can be transferred to other parts of the plant in a matter of a few hours.
Butterworts often have delicate root systems, and many of them, especially in the temperate zones, go dormant in winter and produce hibernacula. These are more difficult to grow in cultivation. Tropical types can grow year-round in a sunny window, greenhouse, or terrarium under artificial lights—most are not exacting as to requirements. Many species and hybrids are available from select growers, so if you have the collector gene, this may be the carnivorous plant for you. Although butterworts are not at all threatening-looking and have an arguably silly common name, they turn out to be very efficient trappers and digesters indeed. You always have to watch out for the quiet, unassuming ones, don’t you?
This excerpt has been reprinted with permission from Bizarre Botanicals: How to Grow String-of-Hearts, Jack-in-the-Pulpit, Panda Ginger, and Other Weird and Wonderful Plants, published by Timber Press, 2010.
