Common Milkweed, Asclepias syriaca, is at first glance merely another pretty roadside wildflower making those long drives a bit more bearable. Growing up to six feet tall, it stands above the jewelweed and Monarda, showing off its spherical umbels of pink-purple blooms as if they were tiny planets orbiting the stem. It even emits a pleasant fragrance, beckoning one to bend and take in its perfume. It is truly one of our most captivating native wildflowers, one of the many Asclepias plants found along the East Coast.
But this showy, seemingly benign plant is in fact quite deadly, with an arsenal full of anti-herbivory weaponry. Firstly, the milky white sap (from which the plant derives its name) is full of glycosides, compounds which are poisonous to many mammals and herbivorous insects, thus deterring them from feeding on the plant. But a few select species have played the “arms race” game with A. syriaca, and thus have evolved to specialize on these plants without experiencing the usual negative side effects. Monarch butterflies, for instance, feed exclusively on plants in the genus Asclepias while in their larval form. As a result of the Milkweed toxins accumulating in the caterpillars, adult Monarch butterflies are poisonous to predators (expect for a few specialists). The bright coloration of Monarchs is thought to serve as an “announcement” of their unpalatability. In addition to its toxicity, the sap of Milkweed contains latex, which functions as a “glue” that traps small insects piercing the stem with their feet or mouthparts, eventually killing them if they cannot pull themselves free. (Both the U.S. and Germany attempted to harvest Asclepias’ latex during World War II as a domestic rubber source, but apparently without much success.)
flowers hide yet another deadly secret. All plants in this genus have an unusual method of pollination: unlike the majority of Angiosperms, which spread their pollen via “dust-like” grains released/carried from anthers, milkweed pollen is contained in “sacs” called pollinia
, within a structure called a pollinarium,
which is contained behind two modified anthers.
Between the two white petals, the two narrow, white modified anthers (here oriented horizontally) create the slit which traps insects’ legs to facilitate pollen transfer. At the top of the slit is the pollinarium gland, and inside reside the pollinia.
When an insect visits the flower to obtain its nectar, a leg may become caught between the two modified anthers, trapping the insect at the bloom with the pollinarium gland attached to its leg. If the insect is strong enough, it will pull the pollinarium from the flower, and upon visiting another Asclepias bloom the structure will be “received” by a special receptor on the flower’s stigma. But many smaller insects cannot pull free. It is thought that this adaptation of Asclepias serves to attract spiders and other predatory insects to the plant, thus deterring damaging, herbivorous insects from visiting the foliage. In the video below, you will see an insect struggling to free itself from an A. syriaca bloom in Buladean, NC.
Nature, in the midst of all her beauty, hides many processes that would pass unnoticed without closer inspection, many of which may at first seem “cruel” or unsavory to those who wish to see the natural world as a peaceful, bucolic scene of wild harmony. But it is not our place to judge the “deviousness” of a flower or the “wickedness” of a spider; we can only observe these as yet another wonder oiling the gears of this great Earthly machine. In this blog I hope to introduce you to some of these wonders (or remind you of them), because even though the beauty of a flower upon first sight will never be bested, once we understand the processes affecting and being affected by this plant, and get a sense of the role it plays in its environmental context, we will have an appreciation that extends to a different, perhaps more meaningful or complex level. And it is with this appreciation and knowledge that we might be able to heal some of the damage that has been done, and hopefully foresee effects of future enterprises before it’s too late.
But a disclaimer: there will still be plenty of pictures simply showcasing pretty flowers.
Catesby’s Trillium; Trillium catesbaei
The rare Large Purple Fringed Orchid; Platanthera grandiflora
Here you can see the devastating effect the hemlock woolly adelgid has had on Eastern Hemlocks (Tsuga canadensis) throughout the Appalachians; only the gray skeletons of these trees remain. This small, sap-sucking bug was accidentally introduced from East Asia during the 1920’s and has killed massive numbers of hemlocks all along the East Coast. The dense evergreen foliage of these trees provide shelter for many species, and their year-round shading of mountain streams maintains the cool water temperatures that trout require. Efforts are underway to stem the tide of this infestation, but pesticide applications are expensive, and biological controls are slow to take hold and have yet to be proven effective at large scales.
Since mid-May I have been working as a field technician in the Southern Appalachians, employed by Dr. Allen Hurlbert at UNC-Chapel Hill. His study is looking at bird communities at sites along a latitudinal gradient, investigating how insect resources and vegetation structure affect species richness and composition. It has long been known that species diversity is spread unevenly along the Earth’s latitudinal gradient, with both diversity and richness generally increasing as one moves from the poles toward the equator. Many theories have been proposed as to why this might be (energy availability, climate harshness, evolutionary rates, etc.), but there is as yet no consensus. Dr. Hurlbert is looking at this phenomenon at a regional scale and hopes to find out whether the amount/diversity of insect food resources and the structure and diversity of vegetation is affecting bird community composition.
Pink Lady’s Slipper; Cypripedium acaule
This lovely native orchid does not produce nectar to entice pollinators, but rather lures bees and other insects in with a strong perfume and showy blooms. The oddly shaped flower has a large tapered hole in its pink pouch, through which the pollinator enters, only to find it cannot exit through the same fissure. In order to escape, they must squeeze through a small hole at the base of the flower, and in doing so first brush against the stigma (built like a comb to remove pollen in case the insect has visited another Slipper) and then against a sticky mass of pollen on the flower’s anther. Duped, they exit the flower bearing a burden but no reward. The unusual fertilization strategy of this plant results in relatively low pollination rates, with fewer than 5 percent of flowers maturing fruit. This, coupled with very exacting environmental requirements, make Lady’s Slippers fairly rare. (Though admittedly beautiful, they almost never survive transplanting, so please do not attempt it.)
The even more elusive Large Yellow Lady’s Slipper; Cypripedium pubescens. This bloom was past its prime, but still very exciting to spot!
Our sites are in Georgia, North Carolina, Tennessee and Virginia. Our “home base” is in the quaint, if touristy town of Highlands, NC, at the Highlands Biological Station. As we are trying to describe the insect resources of each site during different periods of the summer (since there can be “pulses” in food availability, sampling only once would not give an accurate picture of the resources available), the five other crew members and I move around very frequently and are never in one place for more than two nights. In Highlands and our Smoky Mountain sites we have actual beds, but otherwise we are camping.
Making supper in Virginia
My first Walking Stick Insect! Order Phasmatodea
A “true bug,” Order Hemiptera
Fly Poison; Amianthium muscitoxicum. Containing toxic alkaloids, this plant’s bulbs can be crushed and mixed with honey or molasses to attract and kill houseflies. Following pollination, the flowers turn green, as seen on the lower, older flowers in this photo.
Until two weeks ago our efforts were focused on arthropod (insect) sampling and bird counts (done by the bird folks, Katie and Chuck), and now we have started classifying vegetation. Since the vegetation at these sites is changing at a much slower pace than the insect availability, our schedule has calmed down a bit lately, as we only have to visit each site once to describe the forest structure and composition.
Pushing through the dirt like nodding zombies, Indian Pipe (Monotropa uniflora) is always an interesting find. This epiparasitic plant contains no chlorophyll and does not photosynthesize, but rather leeches nutrients from a nearby green, photosynthesizing plant via a “bridge” of mycorrhizal fungi.
The only other plant in the genus Monotropa, Pinesap (M. hypopitys) obtains nutrients by the same method as Indian Pipe, via a mycorrhizal bridge.
Bear Corn (Conopholis americana) is specialized parasitic plant, obtaining nutrients solely from oak trees. It is a favorite food of bears.
If I’ve learned one thing about working on bird projects, it’s that you have to wake up very early. We’re finished with bird counts now, but for most of the summer we needed to arrive at our sites at 6:30, as the birds are most active (an therefore easiest to hear and see) just after sunrise. Depending on where our camp was, this meant waking up anywhere from 3:30 a.m. to 5 a.m. It took some getting used to, but seeing the sun rise over the Great Smoky Mountains is definitely worth it.
The National Park Service has begun to reintroduce elk into the Great Smoky Mountains National Park; here you see a female spotted near the Blue Ridge Parkway (that’s a radio collar around her neck). Once native to the region but driven to extirpation by over-hunting and habitat loss, the last North Carolina elk was thought to be killed in the late 1700s. (Read more about the NPS project here: http://www.nps.gov/grsm/naturescience/elk.htm
Below is a more technical description of our sampling protocol. I realize it may be a bit dry for some, so consider yourself forewarned
Our sites were split into three parallel transects, spaced 250 meters apart, with six sampling stations arranged along each transect. Arthropod sampling consisted of litter, bark, leaf and branch surveys. For litter and bark, we surveyed about a half square meter of ground/bark for five minutes, recording the number of insects we saw and which order they belonged to. (Due to the incredible diversity of North American insects, we only identified these to order and not species.) For leaves, we simply surveyed 50 leaves of any shrub-height plant occurring at the sampling station. Low and high branches were surveyed by capturing a 3-4 foot section of branch in a plastic garbage bag, then at the end of the day we went through the bags, weighing leaf/woody mass and recording any insects we found.
A large millipede (Order Diplopoda), about 9cm long.
One of my leaf surveys included this mass of tiny Arachnids.
Can you spot the Lepidoptera hidden on this tree bark?
In vegetation surveys we’re interested in recording all woody species occurring at the site, and also getting a sense of the structure
of the vegetation – i.e., how much vegetation is at each forest level, from canopy down to shrub, and what species each layer consists of. It has been shown that the structure of forests, sometimes even more than the species comprising them, is very important for birds. In order to get a picture of the structure of a site, we record vegetation heights at 8 random points along 4 transects, at six different stations within the site.
Fire Pink; Silene virginica
Looking down at Chuck from near the top of a hemlock. Sometimes you just gotta climb a tree.
Crimson Bee Balm; Monarda didyma
We also perform a relevé at each station, which is a commonly used method for getting a quick, overall view of a plot’s vegetation; maximum tree height and diameter, canopy openings, elevation, species composition at each vegetation level, and herbaceous cover are a few of the characteristics we record.
Mountain Wood Sorrel; Oxalis montana
Chuck and Annemarie working in a Rhododendron thicket
One of the most amazing (and largest) moths I’ve ever seen, the Tulip Tree Silkmoth (Callosamia angulifera)
It’s all very interesting stuff, and I’ve learned to identify more plants and insects in six weeks than I have during the rest of my 23 years. The biological diversity of this part of the country is astounding, mostly due to the age of the Appalachians and their topographic diversity. It is the oldest mountain chain in North America and supports communities of flora and fauna at a spectrum of elevations, from Spruce-Fir forests down to Chestnut Oak communities. These factors make the Southern Appalachians one of the most botanically diverse regions in the temperate zone, with more than 2000 species of vascular plants. It is also a hotspot for salamander diversity and hosts a startling number of other species. I honestly see a new plant every day I’m in the field.
Lesser Daisy Fleabane (Erigeron strigosus) being visited by what I think is an Orchard Bee
Pygmy Salamander; Desmognathus wrighti. This is an adult!
Our first Black Bear of the season
The dainty Mountain Saxifrage, Saxifrage michauxii
The flower racemes of Galax urceolata
Neighbor Moth; Haploa contigua
Jack-O-Lantern Mushroom; Omphalotus illudens
Tiny fungi; note acorn for scale
You never know where you will see new species. The two moths and dobsonfly below were photographed at a Shell gas station outside of Marion, VA.
Regal Moth; Citheronia regalis
Pandora Sphinx Moth; Eumorpha pandorus
Male Eastern Dobsonfly; Corydalus cornutus. Quite the scary looking insect. There were dozens of these on the outside wall of the gas station.
Rosebay (Rhododendron maximum) is often an obstacle during our workdays, forming dense thickets that are almost impassable. But its blooms make it a little more bearable. “Rhodo hells” became more widespread in the Southern Appalachians following the Chestnut blight (an Asian fungus accidentally introduced in 1904) which killed many American Chestnuts (Castanea dentata), opening up large swaths of forest for Rosebay to colonize.
I have no idea what species this is, but it would take a very brave bird to try and eat this caterpillar.
I recently took a day hike on the Bartram Trail, just outside of Highlands. Named for William Bartram, a Philidelphian naturalist who traveled the Southeast during the 1770s, it runs about 100 miles through NC, but also winds through South Carolina, Georgia, Florida, Alabama, Mississippi, Louisiana and Tennessee, following (approximately) Bartram’s journey from March 1773 to January 1777. The fungi on my trek were incredible; you can see some of them below. (Unfortunately, they aren’t identified; I’m not too good with my mushrooms yet.)
Well, this has been a very long post; I apologize for my procrastination. I’ll leave you with some photos of Flame Azaleas (Rhododendron calendulaceum). Their range of color is spectacular; it seems almost unnatural to come across one of these in the middle of the forest.
Til next time (which will be from the Chihuahuan Desert in New Mexico),