Learning How to Identify Deciduous Trees in Winter
During the growing season, it’s easy to know the name of a tree. The clues are familiar, often learned when we were children. It could be the unique shape of a leaf, like the mittens and gloves of the sassafras, or the autumn color of a sugar maple that gives it away. Perhaps it’s the pink-purple flower that appears as a fuchsia cloud as you roll along the interstate in the spring. Even at 70 mph, that color is so distinctive it could only be a redbud.
Knowing a deciduous tree by name in winter is a different story. After the leaves and flowers fall away, a whole new set of clues is needed. This is a varsity-level horticulture skill, and, I think, a pretty cool party trick to play with the kids during a winter hike. Trust me, there’s nothing like namedropping the good ol’ Acer platanoides to trigger an eye-roll from the teenagers in the group.
One winter I realized I didn’t know my tree friends in their winter garb as well as I used to. To brush up on my skills, I attended a one-day Winter Botany course at Native Plant Trust in Framingham, Mass.
The day began indoors for a few hours of classroom work. A dozen or so other students and I arrived with the required supplies: a hand lens (magnifying glass), ruler, clippers and two "keys." A key is a book that leads you through a series of yes-or-no questions about a plant's characteristics until you arrive at its species. The texts we used were Winter Botany Field Guide and Key by William E. Kuriger, Ph.D. (who taught the class); and Fruit Key & Twig Key to Trees & Shrubs by William M. Harlow, Ph.D.
The classroom tables were piled with dozens of twig and branch samples, which Bill began handing out, one to each of us, while talking about what we needed to look at on each twig to make a positive identification.
Right away we had our hand lenses out, peering at buds, scars (leaf, bundle, stipule) and lenticels. The hand lens brought the tiniest of characteristics into view, which is essential for finding your way correctly through the key. Swapping between lens and book, we checked for the presence or absence of these various marks. For example, the key asked if there are minute, yellow resin droplets on the bark? If there are droplets present, it said, go to #79; droplets lacking, go to #80. Or, count the bundle scars. One scar, go to #3. Three or more bundle scars, go to #12. It felt like we were solving a mystery, and it was fun.
Bark provides clues for identification, such as the size and shape of lenticels, which are clusters of cells that serve as pores for the passage of air. These long, narrow lenticels are of Formosan cherry.
As we stepped through the key, it became clear to me that the tool I should have sharpened before class was my vocabulary. Like any science, botany has its own terminology. Is the bud appressed? Are the bud scales mucronate, valvate, imbricate? Are the stipules persistent? Are the buds scurfy or tomentose? The difference between glaucous and glabrous still throws me. Mercifully, each key had a glossary, and Bill was patient.
A black walnut twig has a tall leaf scar with bundle scars that resemble a monkey's face.
I liked looking at the leaf scars most. The variation between genera is startling, and within the same genus subtle markings tell one species from another. The leaf scars on snowberry (Symphoricarpos) are nearly indistinguishable. Compare it to the leaf scar on a black walnut (Juglans nigra), which is broad and tall, with bundle scars arranged like a little monkey face looking back at you. The leaf scar on a white ash (Fraxinus americana) has a U-shaped notch at the top, but on a green ash (Fraxinus pennsylvanica) it is D-shaped.
Horsechestnut has large, shiny, sticky terminal buds and a shield-shaped leaf scar with a neat margin of bundle scars.
Bundle scars are interesting, too. These little dots indicate the former connection point between a vein and a leaf. They can be numerous, or not. They can be horseshoe or hoof print in shape, as in Philadelphus, or in a single row wrapping around the twig so it looks like a necklace, as in Aralia spinosa.
All the marks I’ve mentioned are on the outside of the twig, but we needed to look at the insides of the samples, too, for important clues. We used the hand clippers to expose the pith. In cross section, the pith can be round, oval or star shaped. Lengthwise, it is either continuous, spongy, chambered or hollow. Pith color varies from white to gray to brown.
We used our fingernails to scratch at the bark, and our noses and tongues to sample the samples. (There were no harmful plants on the table.) Mmmm, minty. Go to #90.
The second part of the day found us putting these skills to use outside in the botanical garden. Bill led us on a tour and pointed out how the trees and shrubs stood out in distinctive and identifying ways:
Perfectly smooth gray bark, light tan leaves that hang on through much of winter and a colonizing growth habit? That’s American beech (Fagus grandifolia). Smooth gray with white bark stretched over muscular-looking vertical bands? That’s American hornbeam (Carpinus caroliniana), also known as musclewood.
This winter, I am motivated to keep this knowledge fresh and continue my learning. The woods near me are mostly oak, beech, maple and hickory. I’ll gather samples from different species within each of these genera and become proficient telling them apart. On an August hike at a local land-trust property, I picked up leaves from at least seven types of oak. Maybe I’ll go back there. But now I won’t need the leaves to know the trees!
Image credits, top to bottom: Shihchuan/CC BY-SA 2.0; Plant Image Library/CC BY-SA 2.0; Shaun C. Williams/CC BY 2.0
