LEARN ABOUT CREATURES

A great activity for winter biology, in places with leaves that fall off trees: identifying twigs. The twigs shouldn't change much for the long winter, so you have lots of time. You can do this indoors, and what you learn makes a landscape of barren trees and shrubs a little more welcoming and approachable.

Background

Scarred twigs

When the leaves fall off the trees each autumn, new scars form. This happens where the leaf used to attach to the branch. In these scars, you can see the holes left over from the veins of the leaves. These holes led water into the leaf and sugar out of the leaf. When the leaf fell off, the holes for these veins closed up and appear as little specks in a scar from where the stem of the leaf connected to the branch.

For every twig, there are different arrangements of these bundle scars. The way the scars are arranged are just one kind of clue about the tree's identity. Other things to notice include buds, "bud scales", "lenticels", "stipule scars", bark, hairs, orientation of buds and more. You look at these signs, and match them up with a special chart that will help you identify the twigs.

The twigs are very beautiful after you look at them for a while. They have wonderful subtle colors, and if you compare a bunch of twigs, you see many differences.

Here's some basic steps to get you started.

1. Go find some twigs from some trees.

   You want to look at the tips of branches. If you cut off the branch of the tree, you will probably want at least a foot (30cm) of twig, because some clues of the twigs identity are found along the whole branch.

   Pruning shears would be good to use to cut the twigs. (I wonder if you can try to root the branch in water as well...we'll have to check. Definitely get a length of twig with at least 3 or more sets of buds.)

   You don't *have* to sacrifice the twig to do this activity if you can find a twig on the ground...but you will want the bud at the very end of the branch as well as a few more.

   It's also possible to do this outdoors, in the freezing cold. You'll need to bring a magnifying glass and your 'key.' We recommend practicing indoors first.

2. Obtain a "key" to woody plant twigs.

   Meaning, a dichotomous key. Botanists use these guides to figure out species in their area. These keys are used for all kinds of species identifications.

   Basically, you start off at "1" and see if your specimen matches. You are always choosing one of two options.

   For my twig, it asks me if my twig has buds that are opposite each other, or if they alternate. I choose one of those ('alternate' for example), and then the next question is 'are there thorns present.'? I answer yes or no...and it keeps going. Many many steps. Do a Google search for 'dichotomous key' and you will see many examples.

   My teacher had us use this key for Minnesota. "Deciduous Trees of Minnesota: a Winter Key" by Thomas Morley. Journal of the Minnesota Academy of Science, Volume 38 Number 1, 1972. (6 pages)

   These keys are specific to places, and usually do not contain all known species. Be careful about native species and ornamental plants - if trees that are commonly planted in your neighborhood are not in the key, you may get really confused.

   It seems pretty frustrating to find these keys through the internet. The keys seem a little proprietary, and trying to sell you a 'winter twig' book (there's a good chance that your public library has a winter twig book, or could get one for you.)

   I noticed that the Department of Natural Resources (DNR) for Minnesota had a reference list, which listed the key that we used in my class. You best bet is to find one of those references and then go to a state university library and look for the reference in the stacks. The public library may not be much help, unless they can get you a copy of the real scientific paper (call them to ask.) Websites aren't very good for this either, so I don't recommend wasting your time. Go to the real university library instead.

   Sometimes it's a little hard to use these keys on your own if you aren't familiar with the plant anatomy.

   I get lost on these keys all the time. Usually, I get stuck because there's always some anatomical feature that is really small and hard to see, or the description is really unclear. Also, my understanding of plant anatomy isn't very extensive. We'll see if we can find some hints for looking up keys online or at a library.

3. Tools

   Get a magnifying lens (7x-10x or more) and a razor blade or craft knife.

4. Learn the parts of the twig.

   The key should have a map to the parts of the twig described.

I just learned how to do this from my Minnesota School of Botanical Art 'Botany for Artists' class with Dr. Robert Bergad. My teacher gave us an assortment of twigs, which we had to identify as our homework. I have been drawing them all.