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Diversity in Amaranth

By Joy Hought, NS/S Research & Education Program Manager. Published on September 20, 2014.

A few days ago we harvested mature stalks from about 15 amaranth accessions at the NS/S Conservation Farm, in preparation for our workshop on October 4th. Melissa, our Conservation Program Manager, then creatively rigged them up back here at the seed bank, upside down in grain sacks to catch any mature seeds as they dry. In our work we talk about diversity all the time, but it’s delightful to see it so clearly in a community of plants that have been stewarded over millennia among different peoples and geographies. It sort of overtakes you when you’re standing amongst them in the field, each one with its own particular beauty.

What stands out the most in amaranth, of course, is the stunning palette of seedhead colors that runs from chartreuse to pale yellow, to mauve, fuchsia, violet and blood red. (NS/S intern Elizabeth recently returned from New Mexico and even reported an orange type.) The color appears mainly in the bracts surrounding the flowers, which eventually dry and reveal pale yellow or black seeds, but is also sometimes present in the stalk and leaves.

If you’ve ever wondered about color in crop plants, like red tomatoes, purple cabbage, blue corn, or orange carrots, you might be familiar with anthocyanins and carotenoids, two of the most common plant pigments. Such “flavonoid pigments” are becoming more widely known as more research shows that they are also rich sources of antioxidants. What’s interesting is that in the Amaranthaceae—which includes beets, swiss chard, quinoa and amaranth but also ornamentals like Celosia—the familiar colorway of violet and yellow is not due to flavonoids at all, but to a completely unique class of pigments called betalains (beta as in beet)—one type causing reddish to violet, a second appearing yellow to orange. Below are a few of the varieties we harvested this week; note the blushed pink tips of Rio San Lorenzo in the center.

Collecting the stalks one type at a time and documenting them with photos is a fast lesson in genetic variation, not only in the expression of pigments in different tissues, but in plant morphology. Natural and human selection have resulted in a very cool array of plant shapes and structures, as seen in the inflorescences (flower heads), stalks, leaves and even roots. The weedy amaranths that grow on the farm have lanky, prickly seedheads and slender, pink-tinted roots that have the familiar earthy smell of beets. In the cultivated varieties, a field of plants that at first glance have very similar spearheads of seed become quite distinct. For example you can see differences in the density and branching of the inflorescences in Moenkopi (below left), Mexican Grain (center) and Guarijio Grain (right).

If we look at the whole plant, some have large inflorescences on multiple branches, while others have been selected over time to have a single flowering stem, which tends to be easier to harvest. You can see this difference in the tree-like Hopi Red Dye on the left and right in the photo below.

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