“This plant, commonly called Venus’ fly-trap, from the rapidity and force of its movements, is one of the most wonderful in the world” and “is one of the most beautifully adapted plants in the vegetable kingdom.”
One of the tree species Mike didn’t include on his recent tree bark quiz, probably because it’s much less common in our area than the loblolly pine, is the longleaf pine. It has the thickest and most resinous bark of any of our pines, the longest needles, and the largest cones. But perhaps most interestingly, at least to me, is the ecosystem that grows up around it.
Longleaf forests once covered up to 60 million acres in the southeastern US, stretching from southern Virginia to eastern Texas. Early explorers and colonists saw dollar signs when they gazed upon the ‘endless’ forest: a source for all sorts of exportable products. The first major economic driver in North Carolina was the naval stores industry – the production of lumber, tar, pitch, and turpentine. Longleaf grow straight and true, making fantastic masts. Their resinous heartwood, called fatwood or lighterwood, was slowly burned under piles of earth, releasing pungent tar. Tar was boiled to thicken it into nearly-solid pitch. Tar and pitch were essential to the sea-worthiness of wooden ships: ropes and sails were soaked in tar, seams in the hull (and pretty much all other wood on a ship) were coated in pitch. The bark of living trees was scraped away, releasing the tree’s natural defense, resin, which was collected and distilled into turpentine. Turpentine had numerous uses, including as a remedy for colds (probably not the best idea). Though the longleaf forest must at first have seemed vast and limitless, after a century or more of harvesting, the once extensive blanket of longleaf pine in the southeast was reduced to about 3% of its original range.
I’ve never been a huge fan of pines. When I lived in Durham, my house was surrounded by huge loblollies, and the yard was ALWAYS covered in pine needles. But a trip to a longleaf pine savanna can change that perspective fairly quickly. Longleaf are so successful in their habitats that they form what at first seems to be almost a monoculture – longleaf, and only longleaf, growing rank on rank as far as the eye can see. They are straight trunked with a waving crown – their lower branches drop off as the tree grows. But if you look a little closer at the dense ground cover, you’ll soon find that the longleaf pine forest is a surprisingly diverse ecosystem.
Some surveys of the ground cover in longleaf savannas have revealed more than 50 species of plants within one square meter. That is more diverse than a rainforest, at a small scale! And in North (and South) Carolina, we have some amazing species that live in that niche. Because of the nutrient poor soils found in longleaf habitats, plants need to have a good strategy for gathering the nutrients they need to thrive. Carnivorous plants have adapted some amazing ways to get nutrients from the ubiquitous insects that also live in this ecosystem. There are 4 primary groups of carnivorous plants in the savanna: sundews, butterworts, pitcher plants, and the most famous of all, the Venus fly trap.
When I saw my first fly trap, I must admit that I was a little disappointed. My high school put on “Little Shop of Horrors” when I was a student there, and Audrey was a pretty impressive, man-eating fly trap. In contrast, the traps of the real plants only get to be about 1 inch in diameter. But if you get down close to them and watch them in action, they are still impressive! The traps are actually modified leaves. They have green or red centers, the mid-rib of the leaf, each with 2-3 “trigger hairs” on the inside of the trap. The traps secrete sweet sap to lure their prey in and are rimmed with thin spines that will prevent escape. The spines look quite vicious, but are in fact more hair-like and won’t hurt you at all if you touch them. When an insect (or a pine needle yielded by a curious observer) touches two trigger hairs in quick succession, the leaf closes, trapping the insect. The repetition is important because the fly trap doesn’t want to be confused and close during every rainstorm! I hadn’t “tickled” a fly trap in a while, so on a recent trip to the savanna, I decided to try it out. Though I’ve done this before, I had forgotten just how quickly the leaf can close! Within less than 1 second it was shut. Apparently, this is one of the most rapid movements in the plant kingdom. Fly traps will reopen after a false trigger like mine, but it may take as much as a day for them to do that. And, they will only close so many times before turning black and dying, so it’s important not to “tickle” fly traps too often. But we typically encourage groups of teachers to try it, as it is an unparalleled educational opportunity to observe this amazing plant species. I filmed this video of a flytrap closing on a recent teacher workshop visit to a longleaf savanna.
Venus fly traps only grow within about a 100-mile radius of Wilmington, NC. Like longleaf, they depend on fire to keep their growing areas clear of taller species that will shade them out (more on fire later). They thrive in ecotones (areas of transition from one plant community to another) at the border between longleaf savanna and pocosins (shrubby bogs of the coastal plain). Because they are so interesting, and so rare, poaching has become a problem for fly traps. About two years ago, North Carolina increased the stakes for fly trap poachers – it is now a felony in NC.
But fly traps aren’t the only show in town. Other types of carnivorous plants also thrive at the edges of the pine savanna, including pitcher plants, sundews, butterworts, and bladderworts. The insect-trapping strategy for each of these is different. Pitcher plants lure insects inside and then trap them in their tubular leaves which are slippery and lined with downward-pointing hairs. The insects can’t escape and the plant exudes digestive juices to claim its nutrients. Purples pitcher plants, Sarracenia purpurea, are a little different – they drown their prey in pools of water.
But even a pitcher plant can’t eat everything that falls in. Frogs sometimes hide out in them, a few species of caterpillar feed on the inner surface of the pitcher, and there’s even a species of wasp that lays its eggs in the shelter of the pitcher. Sundews look a bit like pin cushions that were left out overnight and have been coated by dew. The sweet-smelling droplets are both the lure for prey and the reason for its demise. It is entrapped in the sticky substance, and the leaf rolls up around it. The same sticky secretions also contain enzymes that digest the insect, providing the nutrients the plant is not getting from its environment.
Butterworts are a startling yellow-green color that stands out from the golds and browns of surrounding species in late winter/early spring. Their strategy for capturing prey is similar to sundews. They secrete a sticky substance on the surface of the leaf that lures, traps, ensnares, and digests small insects.
The final group of carnivorous plants found in this type of habitat are bladderworts. Bladderworts are the most varied (species-wise) of our carnivorous plants – there are 14 or 15 species in NC! The bladderworts I have seen in the past are aquatic. Their underwater roots have bladders that suck prey in to be digested. Apparently, there are also terrestrial bladderworts that live in boggy peat soils or moist sand. I didn’t realize this before my trip, so I’ll have to search them out when I return!
Though fly traps have the most limited range of our carnivorous plants, each type is remarkable in its own way and well-worth seeking out in some of the remaining longleaf pine savannas. They’re easy to miss when not in flower, but if you scour the edges where pocosin meets savanna, you might be fortunate enough to find some!