Three Leaves, One Tree - Tales From a Sassafras
Walking through the woods at Harmony Hill as summer begins to wane, we once again notice the hardwood trees. The knowledge that their leaves will begin falling in the coming weeks causes us to take in their beauty as we did in the spring. Though the summer days can be hot, muggy and long, we know that this season can be all too fleeting. And with a couple of cool mornings, Mother Nature has reminded us that we will be saying goodbye to these rather warm days before we know it. With the thought of falling leaves on our minds, we thought we’d take a look at a tree that many simply walk past and stop awhile to revel in its wonder and its complexity. Because, at Harmony Hill, we know common never has to mean simple!
Sassafras (Sassafras albidum) is a common tree throughout South Carolina and is, indeed, the Sassafras used in Sassafras Tea. Sassafras Tea is made by boiling the roots, which extracts both the color and the delicious flavor from the root bark.
Sassafras trees are extremely easy to identify, having three different leaf types growing on a tree. It is one of just a few species in our area that exhibits the ability to grow several different types (or shapes) of leaves. Perhaps we will spotlight another species of tree that does this in a future installment!
The first leaf is a single-lobed leaf that looks exactly like what everyone thinks a leaf looks like. In fact, if you gave a small child a crayon and asked it to draw a leaf, we'd be willing to bet it would look very much like the single-lobed Sassafras leaf.
The second leaf is a two-lobed "mitten" leaf. The name “mitten leaf” is rather fittings, as it looks exactly like a winter mitten, with the thumb sticking out of the larger mitten area.
The third leaf is a three-lobed leaf that is usually equal in size over all three lobes. (Occasionally, there may be a three-lobed leaf with a couple of extra lobes that are reduced in size and near the leaf stem. Depending upon the individual Sassafras tree, they may be anywhere from nonexistent to occurring with some regularity.)
Now, why would a tree grow three different and distinct types of leaves? Well, the answer may be found in WHERE the leaves are found on a tree. Often, the three and two-lobed leaves are found lower on the tree, while single-lobed leaves are found higher on the tree. This is even true on saplings, with the majority of the first leaves being three and two-lobed. It appears that early leaves grow in the presence of more nutrients and starches, which allow for more cell division; thus, allowing those leaves to "branch out" into more lobes. In fact, recalling what we said in the last paragraph, that may very well be the reason it isn’t horribly difficult to find the occasional four or five-lobed leaf mutation of a three-lobed leaf.
Sassafras is in the Laurel (Lauraceae) Family, along with Spicebush (Lindera benzoin). Both plants, along with a few other members of the family, are larval food hosts for the Spicebush Swallowtail Butterfly (Papilio troilus). One of the "Black Swallowtails", some of the finest beauty of this species of butterfly can be found in its larval stages.
Seen in the first and second photos, the caterpillar of the Spicebush Swallowtail looks a whole lot like bird droppings in its early instars. Feeding on leaves out in the wide open is a precarious way to make a living, so it pays to camouflage yourself as best you can. And what better camouflage than to look identical to bird droppings?
Now, another cool thing about this caterpillar is that it transitions in later instars to mimic a tiny snake (and some say, maybe, tree frogs). They will turn from the black and white camouflage of the fecal matter and uric acid of bird droppings to a yellowish caterpillar with late, false eyes. In fact, if you look at the larger end of the caterpillars in the photos, you can see those large black false eyes developing. This imperfect Batesian Mimicry allows the caterpillar to appear to be more than one species that predators don't wish to consume or bother with.
To take the mimicry one step further, as with all swallowtail caterpillars in North America, the Spicebush Swallowtail has a forked organ that emerges from just behind the head, called an osmeteria. They use this organ to deposit foul smelling and tasting chemicals onto potential predators. It also doesn't hurt that its forked and looks like the tongue of a snake!
These caterpillars will spin a silk mat below them, which is visible in both photos, in which they will anchor to. They will then use the silk to roll the leaves up around them as protection.
While Spicebush is its primary larval food source, it readily consumes the leaves of Sassafras. I've also seen it on Red Bay (Persea borbonia) and Swamp Bay (Persea palustris). Unfortunately, Red Bay and Sassafras have been impacted by a fungus introduced into the southeast, (Raffaelea lauricola). This fungus is transmitted by the Ambrosia Beetle (Xyleborus glabratus) and was first documented back in 2002.
Red Bay has suffered large mortalities from wilt brought about by the fungus and Sassafras has been impacted in many areas, as well. Spicebush has been found to also show signs of the disease. The death of these plants and trees has a direct impact on other populations, such as butterflies. The Spicebush Swallowtail is joined by the Palamedes Swallowtail (Papilio palamedes) in relying on members of the Laurel Family.
So, Harmony Hill isn't only a place we work to conserve and protect for beauty and peaceful nature. It is also land which is critical for butterfly species that are on the decline due to disease. Now, next time you're out walking in the woods, and you see rolled up leaves on a Sassafras, smile knowing that Spicebush Swallowtail caterpillars are eating and growing, and they will soon be taking to the air as adult butterflies!
Well, this Nature Note was a little more than we had originally planned. We looked at more than multiple species again, learned about leaf growth, a little about camouflage, mimicry AND we saw how introduced pests can cause serious issues on the landscape, like fungal diseases in native plants.