Polygonaceae (the Buckwheat Family / Rhubarb Family / Smartweed Family / Knotweed Family) has several edible species. Most familiar as commercial foods are Buckwheat and Rhubarb. Some well-known wild foods include Japanese Knotweed, Sheep Sorrel, and Yellow Dock. Usually when someone tells me that they have been learning about wild edibles and have been eating Yellow Dock I tell them to keep learning, as Yellow Dock is quite bitter and is not the most sought-after edible. However, right now in the early spring the leaves have still not developed their strong bitter flavor. In fact, the strongest presence in these leaves pictured, that I was tasting the other day, is a kind of sourness typical of the family such as is found in Japanese Knotweed, Rhubarb, and Sorrel (both Sheep Sorrel and Garden Sorrel).
There are several species of Yellow Dock (the botany of which will be discussed later). Pictured to the right is commonly known as Curly Dock. The picture below is Broad Dock. They are all pretty similar and can be treated with the general name Yellow Dock. The leaves appear early as they grow from a perennial root that is used as a medicinal herb. As a perennial the root becomes very tough and this combined with the strong bitter taste makes the root unsuitable as an edible. The leaves however are commonly known as a source of wild greens. The best way to use Yellow Dock leaves is perhaps including small amounts in salads and cooked foods like soup.