Carnivorous Plants of the Northeast
I spend a lot of time in wetlands of one kind or another and have previously written about carnivorous plants on this blog because I am utterly fascinated by them. This time around I am publishing the writing from a unique organization that I support wholeheartedly (and write for) that promises that any land acquired will never be logged. The Northeast Wilderness Trust has a column called the Wild Times. “Newts from the Field is a seasonal installment written by Wildlands Ecology Director Shelby Perry, bringing the reader the wonders of nature…” The photo of sundews was also taken by her.
“Imagine you are a wild fly, just buzzing along in the world. All around, plants dazzle you with their delights, flowers of lovely colors tempt you with their nectar, and leaves offer you a comfortable resting place. Some of those leaves even have “extra-floral nectaries” where they secrete nectar directly from their stems or leaves, seemingly just for you. These plants appreciate you, maybe because you pollinate them, or perhaps you eat their pests, or you might even help disperse their seeds or spores.
Your environment is full of hazards. Dragonflies zoom overhead like predatory drones that can see in all directions. Spider webs slung through the air lurk ready to net you when you least expect it. And there are any number of insect predators and fungi pathogens that can bring you down at any moment. In this threatening world, the plants seem safe–how could they possibly be a threat to a harmless fly? What could be dangerous about something rooted to the ground that eats sunshine and exhales oxygen? You might start to get comfortable, you’ve been a fly for 15 days (about as senior as flies get). By now you’ve seen it all…right?
Around the world there are over 600 species of carnivorous plants, although calling them all carnivorous might be a bit generous…some of those species are more accurately characterized as coprophages–the technical term for eaters of poo. Here in the Northeast the three most common genera of carnivorous plants are all truly meat-eaters though. They dine mostly on insects, but occasionally also on small amphibians or mammals. These are sundews (Drosera), pitcher plants (Sarracenia), and bladderworts (Utricularia).
The characteristic little green leaves of sundews, bristling with sticky red fuzz (technically called “glandular hairs”) are common sights along wetland edges and beaver ponds in the Northeast. Though there are several species in our region, the two most common are round-leaved (Drosera rotundifolia) and spatulate-leaved sundew (Drosera intermedia).
Like many carnivorous plants, sundews tend to grow in places that are very nutrient-poor, such as bogs. So, they supplement what they can get from their roots with the phosphorous, nitrogen, vitamins, and minerals from the insects they consume. These environments support only very slow growth for sundew plants, and where they grow on bog mats of sphagnum moss they are often overtopped by the moss in the cooler seasons. When this happens they simply send up a central stalk during the next warm season and grow new leaves above the moss.
Though the plants themselves grow quite slowly, there is one way in which sundew growth is quite quick: capturing their prey. When an insect lands on the sticky glandular hairs, its struggle to get unstuck will trigger the hairs and the leaf to bend toward the wriggling insect, sticking it to more and more hairs.
While this might look like movement, the sundew is actually growing towards its prey, by adding cells to the far sides of the leaf and hairs, causing them to curl in toward the insect. The growth rate of these “moving” hairs is much faster when the sundew has captured a live, struggling insect than for a dead one or piece of debris that sticks to the leaf without struggling. It takes roughly 20 minutes for the leaf to enclose live prey, and several hours or more to envelop still objects or dead insects.
There is only one species of pitcher plant native to the Northeast, Sarracenia purpurea, called simply “pitcher plant.” Its characteristic tubular red leaves were originally believed to be a method of storing water by the plant, for use in times of drought. Further investigation has revealed a more interesting purpose: it is a pitfall trap for unsuspecting prey. The hollow leaf has five distinct zones: a flared opening, a smooth neck, a water-filled barrel, a digestion zone, and an area where undigestible bits collect in the very bottom.
The flared opening is bright red in color, with showy veins and nectar glands that beckon hungry bugs in. Downward-facing hairs line the interior, making it very hard for the unsuspecting bugs to go any direction but further in. Below the hairs, the bug will encounter what looks like a smooth leaf surface– respite from the hairs pointing them downward! But what they actually are walking onto is a smooth surface lined with sticky, shingled cells that come off –attaching themselves to the feet of the insect, and further trapping even flying prey. From here their struggle leads them inexorably closer to the fluid-filled barrel of the leaf below. The barrel is filled with water that contains digestive enzymes secreted by the leaf cells that are underwater. The pitcher plant begins digesting the insects as soon as they hit the water. The hairs on this section of the leaf hold prey in place while the nutrients are being absorbed through the leaf. The cell walls here are thinner to facilitate the absorption. Finally, the bits undigestible to the plant collect in the bottom of the leaf. Because nothing goes to waste in nature, there are specialized insects resistant to the plant’s digestive juices who clean up the detritus in the bottom of the leaf.
Bladderworts are probably the most fascinating carnivorous plant you have never heard of. They live all over the world, from the artic to the tropics. There are 14 species local to the Northeast, the two most common being horned (Utricularia cornuta) and common bladderwort (Utricularia vulgaris). They live mostly in bog and wetland environments, and have no roots at all. Instead the plant has a collection of finely divided spreading leaves, which support a single erect flowering stalk. Without their lovely showy flowers, one might not notice the plant at all, which would be a shame since the leaves are perhaps the most interesting part.
Bladderworts’ inconspicuous leaves are dotted with little bladders originally believed to be for flotation or oxygen storage, but now known to be traps. Think of them like the bulbs at the end of eye droppers. They begin convex with their edges sucked in, like the squeezed bulb of the dropper. Near the mouth of the bladder are a series of small “trigger hairs” that let the plant know when prey is moving nearby. Typical prey are isopods, mosquito larvae, and water fleas, but larger bladderwort species can sometimes consume tadpoles or even small fish. When triggered the mouth of the bladder opens, and like releasing the bulb of the eye dropper, anything at the mouth is sucked inside with great speed. Once the bladder is full, and fully rounded, the door is sealed shut again – the whole process taking about two-thousandths of a second.
Carnivorous plants illustrate just one of the myriad ways nature solves complex problems. Forever-wild places ensure that the stage on which evolution plays out will continue to exist into the future, whatever that future may hold. Northeast Wilderness Trust is committed to securing wild places for all of nature’s mysteries, from charismatic mega-fauna, to carnivorous micro-flora, to every living being in between.”