In regards to foraging for edibles, lady’s thumb (Polygonum persicaria) is one of the most easy to recognize plants, which makes it particularly suitable for the beginner gatherer. The thumbprint mark on the leaf of lady’s thumb is really the perfect way to differentiate it from plants similar in appearance. In the center of each lance-shaped leaf is a distinct smudge that looks as if an ink-dipped thumb had grasped the cover of the foliage. Lady’s thumb is located throughout the continental United States, booming as a perennial in U.S. Department of Agriculture plant hardiness zones 2 to 10.
Together with the smudged mark on each leaf, other features make lady’s thumb easily identifiable. During the summer and autumn, the top of the lady’s thumb features arching spikes of pinkish-purple blossoms. The jointed stem often turns red as the season progresses, inspiring another common name, redleg. The leaves climb alternately up the narrow wild plant, which stands between two to three ft in height. Since other members of the Polygonum genus feature jointed stems and pinkish flower spikes, the thumbprint remains the perfect way to distinguish lady’s thumb from its near relations.
Closely related plants also in the Polygonum genus are often called smartweeds. Those common to the West Coast include wild buckwheat (Polygonum convolvulus), pale smartweed (Polygonum lapathifolium), both located in USDA zones 2 to 10. All these are edible, but naturalist Steve Brill notes which smartweed sorts — with the exclusion of lady’s thumb — tend to be extremely strong-tasting and therefore are best used sparingly. As always, make a careful identification of any wild plant you have found and cross-check it with a reputable source before attempting to eat it.
The leaves and flower spikes are the edible areas of the lady’s thumb plant. Since both are so mild-tasting, they are suitable for fresh eating. Add leaves, whole or chopped, to green salads, and use the colorful blooms as edible garnish to green salads or other cold salads. They may also be used like spinach as a side dish, or as a green vegetable at quiche, soups or stir-fries. Boil leaves for 5 to 10 minutes when using lady’s thumb as a spinach substitute.
As an edible plant, the most important value of lady’s thumb may be for its ability to add bulk to your salad or vegetable dish when you are low on greens. According to the internet database “Plants For A Future (PFAF),” lady’s thumb includes natural fibers, sugars, fats and tannins. Nevertheless, it is not high in these or other nutrients and is ranked as of minor nutritional value. Several Polygonum species cause a sensitivity to the sun in some individuals, although lady’s thumb hasn’t been singled out for photosensitivity. PFAF notes which the genus is also related to oxalic acid, which, just like the oxalic acid in rhubarb (Rheum rhabarbarum), hardy in USDA zones 3 to 8), may cause health problems if eaten in huge quantities.