Trifolium dubium
Trifolium macilentum
least hop clover, lesser hop clover, lesser hop trefoil, little hop clover, shamrock, small hop-clover, suckling clover
lean clover
erect to prostrate, branched from base.
erect, ascending, or decumbent, unbranched or branched distally.
pinnate;
stipules ovate, 0.3–0.5 cm, margins entire, apex acute;
petiole to 1.5 cm;
lateral leaflet petiolules to 0.5 mm, terminal leaflet stalk 1–1.5 mm;
leaflets 3, blades obovate to elliptic-lanceolate, 1–2 × 0.5–1.5 cm, base cuneate, lateral veins prominent, ± parallel, ascending, margins dentate distally, apex rounded or retuse, surfaces glabrous or sparsely hairy.
palmate;
stipules lanceolate-elliptic on basal leaves, triangular-ovate on distal leaves, 0.8–3 cm, margins entire, apex acute or acuminate;
petiole 1–15 cm;
petiolules 1 mm;
leaflets 3, blades ovate, rhombic, or lanceolate, 1–4.5 × 0.3–2.5 cm, thin, base cuneate, veins prominent, margins serrate, those of basal leaves setose and/or dentate, apex rounded or acute, surfaces glabrous.
axillary or terminal, 5–20-flowered, ovoid or globose, 0.5–0.9 × 0.6 cm;
involucres absent.
terminal or axillary, 20–40-flowered, ovoid or obovoid, 2–4 × 1.4–3.5 cm, rachis internodes between floral whorls elongated;
involucres absent.
1–1.5 cm.
4–15 cm.
reflexed, 0.2–0.5 mm;
bracteoles a fringe of red setae.
reflexed, to 1 mm;
bracteoles minute, blunt.
2.8–3.5 mm;
calyx campanulate, 1.5–2 mm, glabrous, veins 5, tube 0.8–1 mm, lobes unequal, longer than tube, adaxial 2 shorter, orifice open;
corolla pale yellow becoming brown, 2.6–3.2 mm, not or slightly ribbed, banner persistent, spatulate, 2.6–3.2 × 2 mm, apex rounded to broadly acute.
14–17 mm;
calyx campanulate, 4–5.7 mm, sparsely hairy, veins 10, tube 2–3.5 mm, lobes unequal, shorter than tube, narrowly triangular, orifice open;
corolla violet or deep purple, 14–17 mm, banner ovate-oblong, 14–16 × 8–10 mm, apex rounded or slightly emarginate.
stipitate, ellipsoid, 1.5–2 mm, short beaked.
oblong or clavate, 4–5 mm.
1, yellow or pale brown, ellipsoid, 0.9–1 mm, smooth, glossy.
1–3, brown, flattened ovoid, 2 mm, smooth or slightly roughened, dull.
= 16, 28, 32.
Trifolium dubium
Trifolium macilentum
Trifolium dubium is often confused with Medicago lupulina Linnaeus; the latter may be distinguished by its toothed stipules, deciduous corollas, and shiny, black fruits. Little hop clover may be the co-called shamrock of Irish folklore (E. C. Nelson 1991; P. S. Wyse Jackson 2014); other candidates include other species of Trifolium or species of Medicago or Oxalis.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Trifolium macilentum and morphologically similar species (T. dedeckerae, T. kingii, T. productum, and T. rollinsii) have been treated in diverse ways. J. M. Gillett (1972) recognized the latter four as distinct and considered T. macilentum a subspecies of T. kingii. D. Isely (1998) recognized T. kingii, T. macilentum, and T. productum, and considered T. dedeckerae and T. rollinsii to be varieties of T. macilentum. R. C. Barneby (1989) treated these as two species, T. kingii (with T. productum in synonymy) and T. macilentum (with T. dedeckerae and T. rollinsii as varieties). M. Zohary and D. Heller (1984) recognized T. kingii, with the other four taxa considered subspecies. As treated here, T. macilentum is known from extreme southwestern Utah and adjacent Nevada.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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