Little wetlands of horrors
Predatory plants in Maryland
Predatory, flesh eating, plants. The phrase sounds like something out of a science fiction novel in which bioengineered plants devour humans or beg for food from nerdy florists. While no plants are known to consume humans, more than 670 species and subspecies of carnivorous plants have been known to exist worldwide. Approximately 20 species of these specialized carnivores can be found lurking in the wetlands of Maryland.
So, what exactly is a carnivorous plant? A true carnivorous plant is one that has the ability to capture, digest and absorb animal prey. Carnivorous plant traps can be separated into two main categories: those which are passive or active at catching prey. Passive traps include “pitchers and papers.” These species include plants with pitcher-like traps and plants with sticky, fly paper-like traps.
In contrast, species such as the iconic Venus flytrap use active traps in which sensitive trigger hairs cause the traps to close on their unfortunate prey. The next question that may come to mind is, why exactly are these plants seeking out flesh? Shouldn’t photosynthesis produce all the food a plant needs? Of course, the answer to the latter question is no. Many times, these plants live in harsh environments – acidic bogs lacking essential nutrients, or rainforests rich with hundreds of species all competing for the same set of nutrients. In the simplest of terms, these carnivorous plants mainly eat flesh in order to supplement nitrogen into their diet.
Name that carnivore
Out of the 20 carnivorous plant species in Maryland, 18 of them are native and 2 have been introduced. These carnivores fall into three groups: sundews (Drosera), pitcher plants (Sarracenia) and bladderworts (Utricularia).
Sundews (Drosera) are passive prey trappers. Charles Darwin became so enamored of sundews that he once commented, “I care more about Drosera than the origin of all the species in the world.” These tiny predators use tentacle-like leaves with brightly colored glands to attract and trap prey. Insects that land on the leaves become stuck in mucilage secreted by the glands and are gradually digested by a suite of enzymes and acids. Some species even bend their “tentacles” slowly around their meal. As the sundew’s meal digests, glands on the leaves slowly absorb nutrients. On average, one sundew traps and consumes about five insects per month.
More than 180 species of sundews can be found around the world and on every continent except Antarctica. Maryland contains four species of Drosera, including the Pink sundew (Drosera capillaris), a State endangered plant found in only three places on the Eastern Shore. Pink sundew is only about 2-4 cm in diameter and sports pink flowers in early May. The thread-leaved sundew (Drosera filiformis), named for its thread-like leaves, has been introduced to several bogs in Maryland.
Pitcher plants are the largest carnivorous plant species in Maryland and generally occur in acidic fens and seepage wetlands. The Northern pitcher plant (Sarracenia purpurea) is the only pitcher plant native to Maryland and grows in such limited numbers that it is considered threatened in the State. In contrast, the yellow pitcher plant (Sarracenia flava) has been planted in several areas. Both species passively trap prey by using brightly colored tubes with the sweet scent of nectar. Many of these hungry critters land on the pitcher plant, follow the colorful veins in the leaf and fall in with the aid of downward pointing hairs and slippery cells.
Northern Pitcher Plant (Sarracenia purpurea)
Interestingly enough, the non-biting pitcher plant mosquito (Wyeomyia smithii) has evolved with pitcher plants; its larvae live within the pitcher. The pitcher plant mosquito acts as the top level predator in the pitcher and feeds on parts of animals that the plant cannot digest as well as microscopic organisms such as rotifers. Over 30 species of New World pitcher plants (those in the family Sarraceniaceae) are known to exist worldwide.
Bladderworts (seen below) by far the most sophisticated carnivorous plants, are typically aquatic. Their unsavory name stems from the air-filled sacs or bladders used to lure and actively capture unsuspecting prey. Much of the plant exists as a fine network of bladders and filamentous leaves submerged under the water or a wet substrate like gravel. Because they spend much of their time below a surface, bladderworts are often overlooked until they produce showy flowers that stick out above the water or substrate surface.
Bladderwort bladders are considered one of the most complex structures in the plant world. When water fleas or midges float past and tap specialized trigger hairs on the bladders, a flap on the bladder opens. The plant then uses a vacuum-like force to suck in prey. Once the bladder fills with water, the flap closes and a sugary substance is released to seal both the door and the fate of its prey. This process occurs in one five-hundredth of a second! Over 200 bladderworts exist worldwide.
Maryland has 14 different species of bladderworts, many of which can be found in ditches and open ponds. One of the most unique bladderworts in Maryland is the State endangered swollen bladderwort (Utricularia inflata). This species resembles a floating wheel in the water when it produces its bright yellow flowers.
Throughout the world and in Maryland, many carnivorous plants are rare, threatened or endangered. Carnivorous plants in Maryland face multiple threats. First and foremost, habitat alteration and destruction accounts for the greatest loss of our carnivorous plants. The International Carnivorous Plant Society estimates that as much as 95 percent of carnivorous plant habitat in the United States has been lost.
Carnivorous plants are also threatened by amateur collectors who poach vulnerable populations. Current research also suggests that carnivorous plants are further threatened by poisonous prey contaminated by heavy metals and insecticides.
Carnivorous plants are yet another fascinating example of the rich diversity of life found in Maryland. These plants have evolved over thousands of years to endure and thrive in harsh, unsympathetic environments.
Yet, we risk losing them if we fail to recognize their innate value. As research continues, scientists are discovering plants such as the State threatened purple bladderwort (Utricularia purpurea) are shifting toward using mutual relationships with algae to obtain nutrients rather than consuming prey. Other research is beginning to redefine the concept of plant carnivores. Even those colorful petunias on porches and in gardens have specialized hairs to trap prey. As we learn more about the hidden complexity of plants, we need to ask ourselves, “Is it safe to turn my back on my garden?”
Kerry Wixted is a Natural Resource Biologist and Education/Outreach Specialist with the DNR Wildlife and Heritage Service.