By Nancy Olmstead
What is an individual plant? It’s pretty clear when you are looking at an individual squirrel, or an individual blue jay: it starts at the tail and ends at the head. The question gets harder to answer when you look at some kinds of plants, including many of our New England forest wildflowers. Scientists who study forest plants need to be able to tell one individual from another. If they can’t, their studies might accidentally be made up of many samples of the same few organisms, which would bias the results toward organisms that were sampled multiple times. One example of an understory plant that presents this challenge is Canada mayflower (Maianthemum canadense).
This cute little plant can be found from the arctic to the Atlantic in a broad swath across northern North America, through the upper midwest and the iron belt states, and down the Appalachian mountains to northern Georgia. 
When you’re walking in an upland New England forest during the late spring, summer, or early fall, keep an eye turned toward the understory. You are likely to see a Canada mayflower plant. You might see areas where many Canada mayflower plants grow in a loose patch close to the ground. Some of the plants are just a single, teardrop-shaped leaf growing about four inches above the ground, while other plants have two or three leaves. From late May to late June, you’ll see a crown of 10-30 tiny, white flowers on the plants with multiple leaves. Some of the flowers will turn into reddish, round fruits by summer’s end.
If you gently dig up the base of one of these plants, you’ll find a slender root (or two) that runs horizontally into the soil. If you keep digging carefully, you may be able to follow that slender root right over to a neighboring “plant.” And you could go on to the next “plant,” and maybe to the next, and so on. Eventually, some root connections break down, but they are all the same plant. Canada mayflower has a clonal growth habit – it uses roots like other plants use twigs, to spread out leaves and capture more light. Some clones cover more than 20 square feet; old ones can reach 30-60 years of age.
So what is an individual, and does it matter? Maybe it doesn’t matter to a hiker just admiring the flowers. But for a scientist trying to study plant responses to the environment, it matters a great deal. If we want to understand how plants are reacting to acid rain, or dealing with a changing climate, we have to know where a plant begins and ends. Our questions require us to take independent samples. With molecular techniques, researchers can test individual stems to determine genetic identity. But it’s expensive and time-consuming. Our understanding of these beautiful wildflowers will therefore be limited until we discover an easy way to tell who’s who.