What is the difference between the buckwheat plant that is used as an edible grain, and the wildflowers that are also called buckwheat? Are they related? I saw a plant growing on a ridge in the Olympic Mountains that was later identified for me as cushion buckwheat. Also, are there flowering buckwheats that people grow as ornamentals in gardens?
Edible buckwheat generally refers to Fagopyrum esculentum. If you were to find it growing wild in Washington State, it would be considered an escaped cultivated plant (i.e., weedy). It is sometimes grown as a cover crop, in addition to the use of its ground seeds for buckwheat flour. It is called a pseudograin or pseudocereal because it is not in the grass family (in the same way that amaranth, chia, and quinoa are pseudocereals).
Cushion buckwheat is Eriogonum ovalifolium. Like Fagopyrum, Eriogonum is in the knotweed family—Polygonaceae. There are about twenty native species of Eriogonum in Washington. Many of them grow east of the Cascades. Many more species of Eriogonum are native to California. (This article by Jennifer Jewell, Pacific Horticulture, April 2013 is a good introduction.) Many are best appreciated in the wild. If you want to grow buckwheat ornamentally, try to select a species that suits your garden conditions (ideally, in full sun, in soil that is well-drained and not overwatered, and mulched with gravel). Jewell’s article suggests that penstemon, salvia, and grasses might make good garden companions for the right species of Eriogonum. Plant expert Linda Cochran has experimented with growing a variety of Eriogonum umbellatum in her Olympic Peninsula garden.
Here is some interesting trivia about the scientific names for these different kinds of buckwheat, Eriogonum‘s name is derived from Greek: Erio = wool / gony = knee, referring to hairy nodes of the first scientifically described species E. tomentosum. Fagopyrum comes from Latin fagus (beech) and Greek pyrus (wheat) because the achenes (dried fruits) resemble beechnuts.