Smartweeds, members of the buckwheat family belonging to the Polygonum genus, are often difficult to separate. Two characteristics of these pictured smartweeds identify them as lady’s thumbs (Polygonum persicaria).
First, the leaves are marked with a purplish blotch that someone at some point compared to a “thumbprint”. Second, smartweeds have ocrea which are membranous sheaths encircling the stem at the base of each leaf petiole (stem). The ocrea of lady’s thumbs have stiff hairs, very minute and difficult to see, arising from their tops. Although subjective, the flower spikes of lady’s thumb are also supposedly shorter than the flower clusters of other smartweeds and resemble this plant’s common namesake, a lady’s thumb.
An alien invader from Eurasia, lady’s thumb has established itself in wet sites and moist places throughout most of North America. This annual can become a problem weed in cultivated fields and moist pastures.
Also colloquially known as common smartweed and redshank, among many other names, P. persicaria can grow from one to five feet in height. The erect or spreading stems emerge from a shallow, fibrous taproot. Often red in color, the stems have swollen nodes. Roots can initiate from the lower nodes. The narrow, lance-shaped leaves alternate on the stem and have short petioles. Sometimes the older leaves are slightly hairy. The tiny, five-petaled lady’s thumb flowers are usually varying shdes of pink, but can also be white. The flowers are tightly clustered in terminal spikes at the end of the stems. The fruits are black achenes (dry seeds).
Lady’s thumb leaves and shoots are eaten raw or cooked. I never have tried eating lady’s thumb but should nibble a few leaves someday. Medicinally Native Americans crushed lady’s thumb leaves to ease the itch of poison ivy. An infusion of leaves treated stomach pains while a leaf poultice was said to relieve pain, particularly from rheumatism. According to some researchers lady’s thumb does seem to be helpful in relieving pain, but I did not follow up on the scientific publications since an OTC pain reliever is much simpler. With the appropriate mordants (alum), lady’s thumb can be used as a yellow dye.
Polygonum maculata is another scientific name commonly used for lady’s thumb.
These lady’s thumb plants were growing along the Tule River in Shasta County CA.