Panicled Tick Trefoil
Desmodium paniculatum
Bean family (Fabaceae)

Description: This perennial wildflower is 2–3' tall, sometimes branching in the upper half. The stems are light green and usually hairless; however, some variants of this species have pubescent stems. Alternate compound leaves occur at intervals along the stems; they are trifoliate and their leaflets are extended horizontally in relation to the ground. Individual leaflets are up to 3" long and " across; they are 3-6 times as long as they are wide. Some variants of this species have more narrow leaflets than others. The terminal leaflet is the same length or a little longer than the lateral leaflets. The leaflets are elliptic to oblong in shape and smooth along their margins. Their upper surfaces are medium green and glabrous, while their lower surfaces are pale to medium green and covered with appressed white hairs. The petioles of the compound leaves are up to 2" long, light green, and mostly hairless. At the base of each petiole, there is a pair of tiny deciduous stipules that are linear-lanceolate; these stipules soon wither away. The petiolules (secondary petioles) of the lateral leaflets are very short (less than 1/8" or 3 mm.), while the petiolules of the terminal leaflets are longer (up to ").

The upper stems terminate in either racemes or narrow panicles of flowers. The branches of each inflorescence are light green and covered with hooked hairs. Individual flowers are " long (or a little more), consisting of 5 petals, a short tubular calyx with teeth, an ovary with a single style, and several hidden stamens. The flowers have a typical pea-like structure, consisting of an upright banner and 2 lateral wings that enclose a central keel. The petals are pink to rosy pink; at the base of the upper petal (banner), there are 1-2 tiny patches of yellow. The green calyx is covered with hooked hairs. The slender petioles of the flowers are about " long; they are green to reddish purple and also covered with hooked hairs. The blooming period occurs from mid-summer to early fall and lasts about 1–1 months. There is no noticeable floral scent. Fertile flowers are replaced by flat loments (a type of seedpod) that are about –1" long. Each loment consists of 2-6 rounded segments, a short stipe, and sometimes a short beak. Each segment of a loment is more rounded along the bottom than along the top; it contains a single seed. The loments are covered with hooked hairs. The root system consists of an elongated caudex with fibrous roots. This wildflower spreads by reseeding itself.

Cultivation: The preference is partial sun, mesic to dry-mesic conditions, and sandy or rocky soil.

Range & Habitat: The native Panicled Tick Trefoil is occasional in all areas of Illinois, except the NW section, where it is rare or absent (see Distribution Map). Habitats consist of thinly wooded bluffs, rocky open woodlands, sandy open woodlands, sandy savannas and typical savannas, woodland edges, thickets, rocky glades, and partially shaded roadside embankments. This wildflower is a pioneer species that prefers some disturbance from wildfires, selective logging, and others causes.

Faunal Associations: Long-tongued bees collect pollen from the flowers; these relatively uncommon floral visitors include bumblebees (Bombus spp.), leaf-cutting bees (Megachile spp.), and long-horned bees (Melissodes spp.). Other insects feed on the leaves, flowers, and seeds of Desmodium spp. (Tick Trefoils). For example, the caterpillars of several skippers feed on the leaves: Achalarus lyciades (Hoary Edge), Epargyreus clarus (Silver-Spotted Skipper), Thorybes bathyllus (Southern Cloudywing), and Thorybes pylades (Northern Cloudywing). The caterpillars of the butterfly Everes comyntas (Eastern Tailed Blue) also feed on the foliage, while the caterpillars of the butterfly Strymon melinus (Gray Hairstreak) eat the flowers and developing seedpods. These insect feeders include many kinds of beetles, and some species of thrips, aphids, moth caterpillars, and stinkbugs (see Insect Table). The seeds are eaten by some upland gamebirds (Bobwhite Quail, Wild Turkey) and small rodents (White-Footed Mouse, Deer Mouse), while the foliage is readily eaten by White-Tailed Deer and other hoofed mammalian herbivores. The Cottontail Rabbit also consumes the foliage. The sticky seedpods (loments) cling to the fur of animals and the clothing of humans. As a result, the seeds are carried to new locations.

Photographic Location: A sandy savanna at Hooper Branch Savanna Nature Preserve in Iroquois County, Illinois.

Comments: Among different populations of Panicled Tick Trefoil, there is significant variation in the width of the leaflets and the hairiness of the stems and leaflets. Usually, this wildflower has fairly narrow leaflets, hairless to nearly hairless stems, and hairless upper surfaces on the leaflets. It can be distinguished from other species in this genus by considering the following key characteristics: 1) the narrow leaflets are 3-6 times longer than they are across, 2) the petioles of the trifoliate leaves are fairly long (up to 2"), 3) the deciduous stipules of the trifoliate leaves are small and insignificant, and 4) the leaflets are rather long (up to 3"). Panicled Tick Trefoil is one of the more common species of this genus in Illinois.