In an article titled To Save a Species, Serve it for Dinner (free registration required to read), the New York Times reports on Gary Paul Nabhan's new book,titled Renewing America's Food Traditions: Saving and Savoring the Continent's Most Endangered Foods. Mr. Nabhan has compiled a list of over 1000 endangered American foods, comprising not only heirloom vegetables that gardeners are already keen on, but also American natives used by Native Americans and Europeans alike (pit-roasted antelope, anyone?).
The thing about preserving food species, as gardeners know, is that it isn't about protecting the species and its habitat as it is with preserving most wild species. It's about actually using the plants and animals as food. Heirloom vegetables will only stick around if someone grows them, eats them, and saves the seeds. Heirloom livestock will only exist if someone raises them and breeds them, and that will happen if there's a demand for the meat (or someone has a lot of money to spend on keeping livestock). Just keeping heirloom varieties around as a kind of living museum doesn't work, because unlike wild species, it takes a lot of work to keep them around. That Seneca hominy flint corn doesn't sow itself, ya know.
What's more, successfully preserving heirloom species also involves preserving the knowledge of how to use it. It's hard to get people to save Ny'pa (a kind of salt grass) if they have no idea what to do with it.
The good thing is that many gardeners and small farmers are keenly interested in heirlooms. Many have flavor or other qualities missing from mass-produced supermarket varieties. The tender skins of Brandywine tomatoes, for example, aren't good for shipping, but the winey flavor outshines any pale pink pseudo-tomato you can find in the produce section.
So where do you find heirloom varieties to grow? Some have made enough of a renaissance that they're available in a wide variety of seed catalogs. My two favorites, Territorial and Nichols, carry some, as does Pinetree Seeds. One Green World has a super selection of unusual fruit trees and shrubs. Then there's Heirloom Seeds, an online supplier which features varieties our parents or grandparents grew in victory gardens during the World Wars.
Not all heirlooms make it into the catalogs, though. To find really unusual varieties that haven't reached commercial production yet, turn to the seed exchanges like Seed Savers Exchange. Or ask around the neighborhood to see if gardeners in your area are harboring a local heirloom.
As for that salt grass -- you're on your own there.