To understand the relationships between living things, scientists comb the world's ecosystems, observing, collecting, and analyzing the organisms they find. One of their goals is to identify new species of organisms. Only then can they relate each one to the rest of the earth's family tree.

Classifying organisms is a kind of detective work. It starts in the field—in this case, the jungle of Belize —where scientists make careful notes describing the specimens they study. In the lab, electron microscopes and DNA analysis reveal more of the clues that allow scientists to place each species within a larger ecological picture.

Botanist Nancy Garwood is working on one group of plants, the genus Trema . In the jungle of Belize, she's found two examples from this group of plants. There are similarities, but there are also differences. Do the plants belong to one species or two? Here's what she does to find out:

First, she looks at the plants' ecologies —their relationship to their environment. If the plants need very different conditions in order to survive, they might belong to two distinct species.

And the plants do seem different. Nancy explains.

Read the transcript.

Next, Nancy zeroes in on the plants' physiologies and the processes that allow them to live. Could differences in how the plants produce food mean they are two species and not one?