Desmodium canadense (L.) DC. (showy tick trefoil, Canada tick clover, giant tick clover)

Pl. 395 h, i; Map 1734

Stems 30–100 cm long, erect or ascending, rarely branched, the median portion with a mixture of sparse to dense, hooked and straight, spreading hairs. Petioles of the median leaves 1–3 cm long, progressively shorter toward the stem tip, those of the upper leaves only 0.1–0.8 cm long. Stipules 5–10 mm long, 0.8–1.0 mm wide, lanceolate, angled or slightly tapered to a bluntly or sharply pointed tip, at maturity brown and appressed-ascending or spreading, semipersistent. Leaflets flat or only slightly angled longitudinally, the undersurface with appressed to spreading, straight hairs and often also hooked hairs on the primary veins near the base, the network of raised veins inconspicuous to evident. Central leaflet (3–)5–8(–10) cm long, 1.0–3.5 cm wide, ovate to lanceolate (those of upper leaves narrower), the tip bluntly pointed to rounded. Lateral leaflets 2–7 cm long, 0.5–3.0 cm wide. Stipels 1.5–4.0 mm long. Inflorescences terminal and from upper axils, generally branched, the axis with hooked, multicellular glandular, and sometimes also spreading, straight hairs. Primary bracts 5–10 mm long, narrowly lanceolate, tapered to a sharply pointed tip. Secondary bracts 2.5–3.5 mm long wide, linear. Flower stalks 4–9 mm long. Calyces green or nearly white, sometimes with irregular purple markings, with sparse to dense, straight, spreading hairs and multicellular glandular hairs, as well as dense, very short hairs, the tube 1.5–3.0 mm long, the lobes 3.5–6.0 mm long. Corollas 8–13 mm long, pink or rarely white, the nectar guides pale yellow and white outlined in purple. Fruits straight in outline, the stalklike base 1–2 mm long and concealed by the persistent calyx, consisting of 1–5 segments, each 3–7 mm long and 3.5–5.0 mm wide, rounded above and below with deeper indentations below, uniformly covered with hooked hairs on the margins and faces. 2n=22. June–September.

Scattered to uncommon throughout the state, more frequent north of the Missouri River, apparently absent from the Mississippi Lowlands Division (Northeastern U.S. west to North Dakota and Texas; Canada). Fens, banks of spring branches, and upland prairies; also old fields and roadsides.

This is the showiest species in the genus and is sometimes cultivated in perennial borders, especially in northern parts of Europe and North America, where it is one of the most cold-hardy species.