Description: This native perennial is about 3' tall and normally erect, although it sometimes sprawls along the ground. The green central stem has fine white hairs, sometimes turning brown in response to drought. There are usually a few flowering side stems in the upper half of a large mature plant. The compound leaves consist of three leaflets that are greyish green. Each compound leaf has a short petiole with a pair of small deciduous sheaths at its base. The leaflets are 2-3½" long and less than half as wide. They are oblong or lanceolate in overall shape, but rounded at the tips rather than pointed. Their undersides have fine hooked hairs that cling to clothing or the fur of passing animals. Numerous pink flowers in an elongate raceme occur at the end of one or more of the upper stems. The flowers are about ½" across (as measured vertically), consisting of an upper and a lower petal. These petals are initially folded and keel-like, but eventually open wide, begining with the upper petal. There is a small patch of dark pink at the center of the flower, from which emerges an upwardly curved white tube containing the stigmas and pistil. There is no floral scent. Each flower occurs on a hairy red pedicel, and has a hairy greenish red calyx.The blooming period occurs during mid-summer and lasts about 3 weeks. The flat seedpods have 3 to 5 segments and are about 2½" long. Like the undersides of the leaves, they are covered with fine hooked hairs, and are distributed by passing animals. Usually, the lower side of a seedpod is more rounded than the upper side. Technically, these seedpods are called 'loments.' The root system consists of a taproot that is long, slender, and brown.
Cultivation: The preference is full or partial sun, and moist to mesic conditions. A loamy soil with some organic matter is quite satisfactory. The foliage is often discolored by powdery mildew. This plant increases the nitrogen content of the soil by means of root nodules.
Range & Habitat: Showy Tick Trefoil occurs occasionally in most counties of central and northern Illinois, but is uncommon or absent in southern Illinois. Habitats include moist to mesic black soil prairies, moist meadows along rivers, borders of lakes, thickets, limestone glades, and areas along railroads where prairie remnants occur.
Faunal Associations: The most important visitors of the flowers are long-tongued bees, including bumblebees, Miner bees, and large Leaf-Cutting bees. Some short-tongued bees may also visit the flowers to collect pollen. The caterpillars of the skippers Thorybes pylades (Northern Cloudywing) and Thorybes bathyllus (Southern Cloudywing) feed on the foliage. The flowering stems are a preferred source of food to Papilio japonica (Japanese Beetle), which can weaken this plant sufficiently to interfere with seedpod formation. Like many other members of the Bean family, this plant is highly edible to various mammalian herbivores, including deer, rabbits, groundhogs, and livestock. Some upland gamebirds and small rodents eat the seeds, including the Bobwhite, Wild Turkey, and White-Footed Mouse.
Comments: This is one of the showier Tick Trefoils because of the plentiful flowers, assuming it isn't marred by insects and disease. Showy Tick Trefoil is more attractive when it occurs in colonies, rather than as isolated plants. Distinguishing the different Desmodium spp. is rather difficult. Important features to consider are the number of segments and shape of the loments, and the size and structure of the compound leaves. Showy Tick Trefoil can be distinguished from Desmodium illinoense (Illinois Tick Trefoil) by examining the base of the compound leaves. The leaf-stem (primary petiole) connecting the compound leaf to the stem is much shorter in the former species than the latter species. Similarly, the leafy bracts at the base of the leaf-stem are smaller and more deciduous in the former species than the latter species.