Family: Fabaceae
Tick-Trefoil
John D. Draeger
Key to Wisconsin Desmodium
- 1a.Abaxial leaf surfaces with numerous uncinate (hooked) hairs on the primary and secondary veins; stipules persistent, ovate, slightly clasping at the base 2
- 1b.Abaxial leaf surfaces lacking uncinate hairs (rarely with a few at the base of the midvein); stipules deciduous or somewhat persistent, lanceolate to linear, not clasping 3
- 2a.Inflorescence axis with long, spreading, villous eglandular hairs; stem and inflorescence branched; loments convex above, angled below, 6–11 mm long D. canescens
- 2b.Inflorescence axis with short hairs, some glandular or uncinate; stem usually simple, with a single raceme; loments rounded above and below, 5–7 mm long D. illinoense
- 3a.Midcauline leaves subsessile or with petioles 0.5–2 (–2.3) cm long; abaxial leaf surface pubescence denser on the midvein than on lateral veins; loments rounded D. canadense
- 3b.Midcauline leaves with petioles 2–6.5 cm long; abaxial leaf surface pubescence uniform in density on all veins; loments triangular 4
- 4a.Stems glabrous to glabrate; stipules (6–) 7–12 mm long; corollas 8–12 mm long; stipels (2–) 3–5 (–6) mm long; terminal leaflet ovate, long-tapered to a sharp point D. cuspidatum
- 4b.Stems pubescent to puberulent; stipules (2.5–) 3–6 (–7) mm long; corollas 6–8 mm long; stipels 1–3 mm long; terminal leaflet ovate to elliptic-ovate, the tip acute or blunt, generally not long-tapered D. perplexum
The fruit of this genus is a modified legume, called a loment. It consists of 2 or more 1-seeded, flat, indehiscent segments which are dispersed as separate units. The loments are covered in hooked hairs, and like the fruits of Hylodesmum, easily become tangled in fur or clothing. If a hand lens is not available, one can stick the foliage of a live plant onto one’s clothing; if it sticks easily (due to the hooked hairs) it is most likely D. canescens or D. illinoense. The other three species are less clingy.
