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scorpion ticktrefoil

Habit Herbs, perennial. Herbs, perennial.
Stems

prostrate, 100–200(–300) cm, sparsely to densely patent-pubescent and uncinate-puberulent.

slender, procumbent or decumbent, 20–100 cm, densely patent uncinate-puberulent and/or inconspicuously pilose.

Leaves

trifoliolate;

stipules often caducous, sometimes persistent, ovate or narrowly ovate, 4.5–8 mm;

petiole 28–50 mm;

leaflet blades ovate or rhombic-ovate, lateral veins inconspicuous, arcuate along margin, apex acute or obtuse, surfaces sparsely strigose;

terminal blade 30–70 × 20–50 mm, length 1.4–2 times width.

trifoliolate;

stipules persistent, obliquely ovate, 2–3.5 mm, base auriculate, amplexicaul;

petiole 10–20 mm;

leaflet blades usually ovate to shortly elliptic, rarely narrowly elliptic, apex obtuse, surfaces appressed-pubescent;

terminal blade usually 10–35(–50) × 7–30 mm, length (1.5–)2–3 times width.

Inflorescences

lax-flowered, ascending, terminal and branched, also axillary and unbranched;

rachis uncinate-puberulent;

primary bracts caducous, ovate, 3–4 mm.

lax-flowered, terminal and axillary, usually unbranched;

rachis densely spreading-pubescent;

primary bracts caducous, narrowly ovate, 1.5–2 mm.

Pedicels

7–9 mm.

3–10 mm.

Flowers

calyx 2.5–3.5 mm, uncinate-puberulent, tube 1 mm;

abaxial lobes 2 mm, lateral lobes 1.5 mm;

corolla purple, 8–9.5 mm.

calyx 1.5–2.5 mm, pilose, tube 1 mm;

abaxial lobes 1.5 mm, lateral lobes 0.7–1 mm;

corolla lavender-pink or reddish purple, banner with yellow spots, 4–5 mm.

Loments

sutures obtusely dentate abaxially, sinuate adaxially;

connections adaxial, 1/4–1/3 as broad as segments;

segments 3 or 4, deltate-rhombic, 6–8 × 4–5 mm, obtusely angled abaxially, straight or slightly convex adaxially, uncinate-pubescent;

stipe 2 mm.

turgid, straight or curved, linear;

sutures equally shallow-undulate;

connections central, 2/3–3/4 as broad as segments;

segments 5–10, narrowly oblong or narrowly elliptic, 4–5 × 1.5 mm, rugose, not reticulate, symmetrically convex abaxially and adaxially, densely uncinate-pubescent throughout;

stipe 1 mm.

Desmodium ×humifusum

Desmodium scorpiurus

Phenology Flowering summer–fall. Flowering year-round.
Habitat Woodland openings and edges, powerline cuts, near exposed limestone. Waste places, lawns.
Elevation 0–300 m. (0–1000 ft.) 0–10 m. (0–0 ft.)
Distribution
from FNA
CT; DE; IN; MA; MD; MO; NJ; NY; PA
[BONAP county map]
from FNA
FL; Central America; South America; Mexico (Durango, Guerrero, Guanajuato, Jalisco, Michoacán, Oaxaca, Sonora, Veracruz); West Indies [Introduced in North America; introduced also in Asia, Africa, Pacific Islands, Australia]
[BONAP county map]
Discussion

Desmodium ×humifusum had been recognized as a species, but J. A. Raveill (2002) confirmed a hybrid origin from D. paniculatum and D. rotundifolium by allozyme electrophoresis. Desmodium × humifusum is likely to occur more widely than reported. It is in the Center for Plant Conservation’s National Collection of Endangered Plants as D. humifusum.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Source FNA vol. 11. FNA vol. 11.
Parent taxa Fabaceae > subfam. Faboideae > Desmodium Fabaceae > subfam. Faboideae > Desmodium
Sibling taxa
D. arizonicum, D. batocaulon, D. canadense, D. canescens, D. cinerascens, D. cuspidatum, D. floridanum, D. grahamii, D. gramineum, D. illinoense, D. incanum, D. intortum, D. laevigatum, D. lindheimeri, D. lineatum, D. marilandicum, D. metcalfei, D. nuttallii, D. ochroleucum, D. paniculatum, D. procumbens, D. psilocarpum, D. psilophyllum, D. retinens, D. rosei, D. rotundifolium, D. scopulorum, D. scorpiurus, D. sessilifolium, D. strictum, D. tenuifolium, D. tortuosum, D. triflorum, D. tweedyi, D. viridiflorum
D. arizonicum, D. batocaulon, D. canadense, D. canescens, D. cinerascens, D. cuspidatum, D. floridanum, D. grahamii, D. gramineum, D. illinoense, D. incanum, D. intortum, D. laevigatum, D. lindheimeri, D. lineatum, D. marilandicum, D. metcalfei, D. nuttallii, D. ochroleucum, D. paniculatum, D. procumbens, D. psilocarpum, D. psilophyllum, D. retinens, D. rosei, D. rotundifolium, D. scopulorum, D. sessilifolium, D. strictum, D. tenuifolium, D. tortuosum, D. triflorum, D. tweedyi, D. viridiflorum, D. ×humifusum
Synonyms Hedysaum humifusum, Meibomia humifusa Hedysarum scorpiurus, Meibomia scorpiurus
Name authority (Muhlenberg ex Bigelow) L. C. Beck: Bot. North. Middle States, 86. (1833) — (as species) (Swartz) Poiret in F. Cuvier: Dict. Sci. Nat. ed. 2, 13: 110. (1819)
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