Trifolium dubium
Trifolium stoloniferum
least hop clover, lesser hop clover, lesser hop trefoil, little hop clover, shamrock, small hop-clover, suckling clover
running buffalo clover
erect to prostrate, branched from base.
creeping, branched, rooting at nodes.
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, opposite or subopposite on erect stems;
stipules lanceolate (on prostrate stems) or ovate (on erect stems), 1–2 cm, margins entire or shallowly serrate, apex acuminate;
petioles 6–15 cm on prostrate stems, 0.5–4 cm on erect stems;
petiolules 1 mm;
leaflets 3, blades broadly ovate or obcordate, 1–2 × 0.5–2.5 cm, base broadly cuneate to rounded, veins fine, margins serrate, apex emarginate or rounded, surfaces glabrous.
axillary or terminal, 5–20-flowered, ovoid or globose, 0.5–0.9 × 0.6 cm;
involucres absent.
terminal, single or paired at tip of upright stem, 15–30-flowered, globose, 2–3.5 × 2–3.5 cm;
involucres absent.
1–1.5 cm.
2–7 cm.
reflexed, 0.2–0.5 mm;
bracteoles a fringe of red setae.
elongated and strongly reflexed in fruit, 2–5 mm;
bracteoles lanceolate, 2 mm.
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.
9–15 mm;
calyx campanulate, 4–7 mm, glabrous or sparsely pubescent, veins 10, tube 1.3–3.3 mm, lobes subequal, subulate, orifice open;
corolla white, veins often pinkish, 8–14 mm, banner ovate or oblong, 8–14 × 4–5 mm, apex rounded or emarginate.
stipitate, ellipsoid, 1.5–2 mm, short beaked.
oblong, 2.5–3 mm.
1, yellow or pale brown, ellipsoid, 0.9–1 mm, smooth, glossy.
1 or 2, tan to brown, reniform, 1.3–2 mm, smooth.
= 16, 28, 32.
= 16.
Trifolium dubium
Trifolium stoloniferum
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 stoloniferum was thought to be extinct but was rediscovered in the early 1980s (R. L. Bartgis 1985). It is now known from extant populations scattered throughout much of its original range, in five of the original eight states in which it was found historically (D. J. Crawford et al. 1998); it was discovered in Greene County, Pennsylvania, in 2017, but appears to be extirpated in Arkansas, Illinois, and Kansas. R. J. Hickey et al. (1991) examined genetic diversity of T. stoloniferum populations using allozymes and found low diversity, with some populations appearing genetically uniform. Molecular studies using RAPDs (Crawford et al.) indicated somewhat higher genetic diversity, even in relatively small populations.
Trifolium stoloniferum is in the Center for Plant Conservation’s National Collection of Endangered Plants.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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