The Carlisle Mosquito Online

Friday, February 15, 2008

Features

Biodiversity Corner - Butternut, or identifying trees in winter

Since the fall I have been wondering about a broken tree at the edge of the Towle Field. The tree is wrapped around with oriental bittersweet, an invasive and destructive vine which almost certainly contributed to the tree's demise.

The four-to-five-inch butternut twig held enough information to identify the tree. (All photos by Kay Fairweather.)

Last Saturday, February 9, Concord- Carlisle Community Education ran a "Botanical Tour of the Towle Land" led by Michele Grzenda, who showed us how to identify trees and shrubs in winter. By the time we came to the broken tree, about an hour into the tour, she had already taught us many of the signs you can use to identify trees without leaves. She then took us through the questions from her dichotomous key, and together we identified the tree as a butternut.

Name. Butternut is also known as white walnut and sometimes as oilnut. The scientific name is Juglans cinerea. The genus name Juglans comes from the Latin words Jovis meaning Jupiter and

Visible here are the chambers in the pith, an important component in identifying the tree.

glans meaning nut and indicates a nut fit for a god — which would better describe the black walnut, Juglans nigra, than this species. And it gets worse. Cinerea comes from the Latin cineris meaning dust or ashes and refers to the gray color of the bark, but we ignore that and call it the white walnut — or in the spirit of Monty Python, something completely different, like butternut.

Clues for twig detectives. A large part of identifying trees in winter is knowing what to look for. In addition to obvious things like silhouette, growth pattern, bark and habitat, a lot of the visual indicators involve twigs and in particular the buds — their position, size, color, shape, scales and fuzziness. My favorite visual sign is the shape of the leaf scar, the mark left on the twig when the leaf falls off. Visual signs can also include secondary indicators like evidence of caterpillars (e.g., tent caterpillar remains on the black cherry) and species-specific fungi (e.g., cedar-apple rust on the eastern red cedar). But the clues are not all visual. You can use more than look-and-see — we got into scratch-and-sniff, chew-and-taste, and touch-and-feel.

Distinguishing characteristics. The combination of characteristics that distinguish the butternut are alternate buds, a terminal bud which is longer than it is broad, cross-partitions in
This is the "monkey face" peering out from the leaf scar of the butternut.
the dark brown pith, and the "monkey-face" leaf scar with its shaggy uni-brow. The eyes and mouth in the monkey face are bundle scars left by the veins which had carried sap and food in and out of the leaves. While the shape of the leaf scar and the three bundle scars within it are indicative of a walnut, the unibrow ruled out the black walnut.

Similarly, the chambered pith is a feature of both black walnut and butternut but only the butternut has dark brown pith. It was possible to identify this tree from just four or five inches of a leafless twig.

Sources. Concord-Carlisle Community Education instructor Michele Grzenda, conservation agent for the Town of Framingham; Winter Tree Finder, May T. Watts and Tom Watts (this book had the key we used in the field for the butternut); Trees of the Eastern and Central United States and Canada, William M. Harlow; Virginia Tech College of Natural Resources at www.cnr.vt.edu (search for "twig key"); Tree Identification Book, George W. D. Symonds.


2008 The Carlisle Mosquito