On a warm and humid mid-afternoon, I roamed Piney Woods Church Road, in search of new discoveries and possible images. Near Rico Road, I found an circular web with this jewel of a spider waiting patiently for her prey. She is a female orchard orbweaver (Leucage venusta), a relatively common orb spider of the Eastern forest, notable for a prominent orange-red horseshoe on the underside of her abdomen.
Join me on a Georgia roadside walk in mid-spring, and let us see what flowers we might gather in honor of Mother’s Day. Most wildflowers of the rural road edges do not hold up well cut and placed into a vase; they thrive better where they grow, in ditches or along embankments. For this reason, we will seek instead a photographic bouquet, which lasts far longer and (in the case of our thistle species, at least) is far less prickly. One of our first discoveries, perhaps because it is so abundant, is a plant with stalked clusters of yellow flowers, vaguely reminiscent of a brown-eyed Susan without the brown eye and with fewer petals. The basal leaves of the plant are somewhat elliptical in outline and highly serrated. The plant is Southern ragwort, also called Small’s ragwort (Senecio anonymus), a member of the Aster or Sunflower Family. Although used medicinally by Native Americans, this native plant has been found to contain toxins that can cause a number of ill effects, and should best be appreciated for its visual qualities only.
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Continuing down the dusty gravel road, we pass an extensive grassy area filled with flowers that look like over-sized dandelions. They rise above the ground up to two feet on their slender stalks. Their leaves are all in a rosette at the base, and look nearly identical to those of the dandelion, only a bit larger. The plant in question is the rough cat’s ear (Hypochaeris radicata), a Eurasian plant that is now widespread across the United States. Unlike the ragwort, this plant is a worthy salad additive; both the young leaves and the flower heads can be eaten raw.
Next we encounter a clump of low, clover-leaved plants, each having bright yellow heads that with forty minute florets each. Called low hop clover (Trifolium campestre), the plant is a Eurasian native that has become established throughout the United States. Because it is a legume (a member of the Bean or Pea Family), it helps to add nitrogen to the soil. (Nitrogen is a nutrient necessary for plant growth.) As the flower head dies, the florets all droop downward, making the head appear like dried hops. While blooming, the flowers are frequented by honeybees.
Our next discovery is an inconspicuous plant with minute, five-lobed white flowers, having a most distinctive name. Called beaked corn salad (Valerianella radiata), it can be identified by its forked stem with sessile stem leaves (meaning that they are attached directly to the stem, without a petiole). Its name originates from its habit of growing wild in corn fields. The leaves make an excellent salad ingredient, with a delicious nutty flavor. The European corn salad (Valerianella locusta) is nearly identical but has pale blue flowers. A popular green, it is also called lamb’s lettuce.
Our Georgia roadside walk would not be complete this time of year without spotting one thistle blooming in a pasture or roadside ditch (or, as cattle farmers who consider it a noxious weed would prefer to call it, a “blooming thistle”.) Closely related to artichokes, thistles are almost entirely edible, from their roots and leaf ribs to their flower stalks and flower heads (equivalent to the artichoke heart). They are edible, that is, if one has a lot of patience, a lot of time, and a lot of thistles. For our purpose, this purple bull thistle from Eurasia (Circium vulgare) will add a splash of vibrant color to the whites and yellows of our bouquet.
Today was my first day “in the field” with my new Olympus OMD EM5 camera. I still look fondly upon the Sony CyberShot that I used for the first 127 days. But this new camera leaves me amazed with the vividness of color and crispness of images possible. I am still figuring it out — there is so much to learn! Today, I share this image of a leaf miner’s “scrawl” on a leaf of muscadine grape, reminding me of scrimshaw work.
Now that all of our deciduous trees are in leaf, and roadside ditches and forest floors in the Georgia Piedmont are green with life, it is a marvelous time to take a walk and see how many different leaf shapes you can find. Many shapes are particular to a certain kind of tree, shrub, or vine; some, like that of the maple, have even been celebrated on a country’s flag. There are the three jagged leaflets of poison ivy, and five of Virginia creeper; the many lobes (rounded or jagged) of the oaks; the tulip-shaped leaves of the tulip tree tree; the five-pointed star of the sweet gum; and the heart-shaped leaves of the wild yam. Some plants cannot settle upon one leaf shape, but instead have several. Leaves of the sassafras tree can be simple ovals, shaped like mittens, or have three broad, blunt lobes.
It is one of those wonders of the natural world that there is such diversity in the shapes of leaves. As one website on leaf shapes remarks, “Plants have leaves in many different shapes – the thicker the book you refer to, the more leaf shapes they seem to find.” The various classifications and permutations of shape form an arcane language, limited to a handful of botanists and elementary Montessori school students: terms such as runcinate, trifoliate, cordate, digitate, and deltoid. Although the words may be unfamilar, they describe the shapes of leaves encountered all around us: dandelion, clover, morning glory, maple, cottonwood. Beyond terms for general shape are further classifications for leaf form: toothed or untoothed, simple or compound, entire or lobed. Finally, even though one set of terms might be used to classify a leaf from a particular species of plant, some plants, particularly oaks, have leaves that vary considerably while keeping to generally the same overall shape.
Why? Why is there such diversity in leaves? What makes one leaf angular and another rounded, one leaf wide and another narrow? These are the kinds of questions wondering children might ask, after being satisfied with a general explanation for the color of the sky and the forces causing the wind to blow. And, like most questions children generate, the answer is not an easy one. Indeed, there is no one clear explanation out there. Only a few days ago, a physics blog reported a new theoretical model that purports to explain all leaf shape variation as an incidental effect of the different patterns of veins in the leaf.
Some aspects of leaf shape have been explained based upon comparing tropical forest plants with temperate forest ones, such as those here in Georgia. A visit to a tropical rainforest, or a greenhouse full of tropical plants, will reveal that most tropical leaves are thicker than temperate ones, as well as more rounded and smooth-edged (untoothed). Tropical plants retain their leaves for years, while deciduous plants in Georgia forests all keep their leaves only for one season. As a result, tropical leaves are sturdier than temperate forest ones, and therefore thicker. Thinner leaves require less energy to produce, and are more effective at gas exchange needed for photosynthesis. However, there is a cost of having thinner leaves: they are not as sturdy, particularly in areas distant from the major leaf veins (which provide structural support for the leaf). So those distant areas are simply done away with, resulting in lobed leaves like those of the white oak. The lobes (or teeth) of many leaves of Georgia plants also help to reduce wind resistance (and the damage that could result from it). Also, botanists have noticed that lobed or toothed leaves can permit sunlight to reach leaves beneath them, so perhaps the indentations help the plants filter sunlight down to leaves on their lower branches or stems.
Ultimately, we simply do not know why there are so many leaf shapes are out there, and how (if at all) a star-shaped leaf might better serve a sweet gum tree’s needs than the compound structure of ovate leaflets of a hickory. It is humbling and perhaps even a bit comforting, though, that something so commonplace as the forms that leaves take has managed to remain so mysterious for so long a time.
This article was originally published on May 8, 2010. The original photo has been replaced with a recent one I took, of a sassafras leaf.
I set out down Piney Woods Church late this afternoon with lifted spirits, following an encouraging note from a friend, reminding me that all the changes I saw yesterday will soon be undone by nature, in the form of rain, wind, and new growth. Meanwhile, I discovered all sorts of possibilities for photographs today. The image I selected is a close-up of the point where the leaf of a vine connected to the main stem. It marks a confluence, where all of the veins in the leaf come together. Also at the join, two long trendrils emerge from the plant, helping it to climb over any obstacles and cling to anything in its path. Most likely, the plant is one of two possible species (both invasive) in the genus Discorea: either the air-potato (Discorea bulbifera) from Africa, or the Chinese yam (Discorea oppositifolia) from Asia. The two are difficult to distinguish (my bets are on the Chinese yam), but both plants are considered highly invasive.
One thing I have noticed from all my explorations of roadside plants is that most of them are non-native, and they harken from a variety of homelands. Many are from Europe, but others are from parts of Asia or even Africa. I am coming to realize that a rural Georgia back road can be a much more cosmopolitan place than I had previously imagined.
Once I identified this roadside plant as Indian strawberry (Duchesnea indica), I naturally assumed it to be a native one, somehow associated with American Indians. Instead, this creeping plant with three serrated leaflets and prominent, five-petaled yellow flowers has become naturalized from India. As the National Audubon Society’s Guide to Eastern Wildflowers notes, the plant is decidedly “strawberry-like”. Its fruit’s taste is, to quote Wildflowers of Tennessee, the Ohio Valley, and the Southern Appalachians, “dry and not pleasing.” Indian strawberry is common to waste places and lawns throughout the eastern half of the United States.
Patience rewarded me at last. After hearing a bird making the same insistent brief call from the foliage, I spent several minutes trying to locate the source. At last, I found a small, rather elusive brown bird, skipping from spot to spot among the branches of vines and trees. I was able to snap a couple of quick photographs before the bird disappeared from sight. My wife informed me that it was almost certainly a wren, and my Birds of Georgia field guide photograph of a Carolina Wren (Thryothorus ludovicianus) is nearly an exact match. The Carolina Wren is a cavity-nesting bird that resides year-round in Georgia.
On my way back down Piney Woods Church Road toward home today, I stopped to visit with a neighbor and dear friend. He showed me his native azalea, in full bloom along the side of his house. As we stood there admiring its showy, brilliant orange blossoms and delicate, honeysuckle-like scent, a large moth appeared. I had never seen its kind before; it had brilliant black and yellow banding on its abdomen. Several field guides and a Google search later, I determined that it was a Nessus Sphinx moth (Amphion floridensis). Common throughout the eastern United States, this moth is fairly unusual for being active during the daylight hours, feeding on the nectar of various plants. The caterpillar larva’s host plants include amplelopsis, cayenne pepper, and grapevines. Considering the local habitat offerings, I suspect that it fed on wild grape leaves.
On my Piney Woods Church Road saunter this morning, I encountered two new “common weed” wildflowers in bloom: the low hop clover (Trifolium campestre) and field madder (Sherardia arvensis). The low hop clover is a yellow flower native to Eurasia now common in most of North America; introduced by farmers to improve the soil and feed their livestock, low hop clover is also a wild edible plant. Field madder, also from Eurasia, commonly grows in farm fields and along road edges throughout the Eastern United States. It has minute flowers that are less than an eighth of an inch across. I only noticed it because I was sitting on the ground in one spot for several minutes, during yet another attempt to photograph a lobelia growing alongside a barbed wire fence.
While struggling (and largely failing) to take an interesting photograph of Chinese privet flowers, I caught this pair of ladybugs mating on a leaf. It’s springtime, and love is in the air. My wife suggested that this could make a great Valentine’s Day card, but I am not as certain.
