Stepp remembered that years later when he was working as an instructor at the University of Georgia. As a research project, he had his students collect plants alongside a railroad track, and in a dense forest. They identified all the plants, and checked to see which ones were used historically by Native Americans.
"We found very few in the forest," Stepp says. "But we found a huge number alongside the railroad track."
Like the Mayans, those early Americans found weeds to be the most helpful in treating their maladies.
It all makes sense, Stepp says, when you consider the plight of the weed. Easy prey for foraging animals and insects, weeds thrive because they came up with ways of protecting themselves.
"Weeds developed defense compounds that protect them from animals and insects," Stepp says.
Generally, those compounds make weeds taste bitter. That's one of the ways that early Mayans figured out which plants might have medicinal value.
"Taste is a big marker," Stepp says. "That's usually an indication that they might have some medicinal value. Probably the most important class of compounds for medicinals are alkaloids and alkaloids generally tend to be bitter. So just by tasting it, you can figure out that this plant has alkaloids in it, and alkaloids often are useful medicinally."
Of course, that procedure probably had disastrous results for some early experimenters. Some plants are very toxic if eaten, like brugmansia, or "angel's trumpet," which is mashed into a paste and used by the Mayan to reduce swelling. It works if applied externally, Stepp says, but it's poisonous when eaten.
So Stepp doesn't recommend that we venture forth and eat weeds. But he does suggest that researchers pay a little more respect to plants that are cursed and despised by gardeners around the world.
Even the voracious dandelion suffers from an unfair rap, he says. The Mayans use it to treat colds, and Native Americans boiled it into tea.
Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.