Goat’s-rue (Tephrosia virginiana) of the Pea (Fabaceae) Family occurs throughout the eastern U.S. from Texas and Minnesota to the Atlantic, except for Vermont and Maine. In Arkansas, it occurs mostly statewide except for counties along the Mississippi River. Other common names for goat’s-rue include Virginia tephrosia, catgut and devil’s-shoestrings. The genus name, Tephrosia, is based on the Greek word tephros meaning “ash-colored” or “hoary” due to the white or grayish hairs covering the plant. The name “goat’s-rue” is based on the plant having been fed to goats with the belief that it increased milk production, but that use has been discontinued. The name “devil’s-shoestrings” relates to the plant’s long, tough fibrous roots. This plant, as does many other plants in the Pea Family, has a symbiotic relationship with a soil bacterium (rhizobium) whereby the plant converts (fixes) atmospheric nitrogen to a usable form within root nodules.
Goat’s-rue is an herbaceous perennial legume favoring sunny sites with sandy to rocky, dry soils of glades, open woodlands and prairies, generally on acidic soils. Plants consist of sparingly branched stems bearing odd-pinnate compound leaves and that terminate with an inflorescence of pea-like flowers. Stems, from a caudex, can be several or numerous. Early growth of plants have an overall light green color which changes to grayish green with maturity due to plant hairs. Hairiness varies from a fine, soft pubescence on upper leaf surfaces to densely hairy on stems and seed pods. Plants, up to two feet tall, tend to recline later in the growing season.
Photo 1: Early spring growth of goat’s-rue in a rocky and sunny glade.
Compound alternate leaves are odd-pinnate, having 14 to 24 lateral leaflets and one terminal leaflet. Leaflets, up to an inch long and ¼ inch wide, are oblong to narrowly elliptic with entire margins and gradually terminate at a sharp tip. Lateral leaflets tend to be opposite, but may be offset across the rachis (main axis of leaf). Leaves have short petioles (attachment of rachis to stem) and leaflets have short petiolules (attachment of leaflet to rachis). The upper surface of the rachis has a central grove. Central veins of leaflets are prominent on the under sides.
Goat’s-rue blooms in late April or May, with the inflorescence consisting of dense racemes several inches long at the tops of the stems. Five light green sepals are fused to form a calyx with five teeth. The calyx is densely hairy on the outside, as are the pedicels and stems. Buds and flowers face in all directions around the inflorescence. Bicolored, pea-like flowers, ¾ inch long and across, have a broad upright petal (banner or standard) in shades of cream and yellow and a pair of lateral, forward projecting petals (wings) that are deep rosy pink. The wings enclose a pair of smaller petals fused at their apex to form a keel which encloses ten stamens and a pistil.
Photo 2: Close-up of goat’s-rue inflorescence showing hairiness of plant and bicolored flowers.
Photo 3: Goat’s-rue plant at peak bloom.
Fruit, which form in mid-summer, are flattened, 2-inch long hirsute pods situated on the stems in widely spreading fashion. They are initially light green, but later turn brown with maturity. The pods contain flattened, kidney-shaped mini-beans. When mature and dry, the pods split, with the halves twisting in a cork-screw fashion, ejecting seeds a short distance.
Photo 4: Densely pubescent seed pods of goat’s-rue firmly fixed in various directions from stem.
Goat’s-rue is a beautiful native plant that looks attractive in a natural setting or a sunny garden with well-drained soil. Nectar, pollen and leaves attract leaf-cutting bees and other insects. However, plants may be difficult to establish from seed or pots, and they are extremely difficult to transplant due to their large roots. The plant contains rotenone (used as an insecticide and to kill invasive fish) and should be considered toxic to people and many animals.
A second member of this genus also occurs in Arkansas: hoary-pea (Tephrosia onobrychoides). It is found in prairies and fields of the West Gulf Coastal Plain and Arkansas Valley. Flowers of hoary-pea are smaller and occur widely spaced in racemes on tall stems held well above the leaves. Leaves and leaflets, too, are more widely spaced than in goat’s-rue. The solid-colored flowers of this species start out as pale pink to almost white when flowers first open but then change to a deep rose-red as the flowers fade.
Article and photographs by ANPS member Sid Vogelpohl