Trifolium dubium
Trifolium polyodon
least hop clover, lesser hop clover, lesser hop trefoil, little hop clover, shamrock, small hop-clover, suckling clover
Pacific grove clover, woods or Pacific grove clover
erect to prostrate, branched from base.
decumbent or ascending, branched.
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 to ovate, 0.4–1.8 cm, margins lacerate, apex acute to acuminate;
petiole 0.5–6 cm;
petiolules to 1 mm;
leaflets 3, blades broadly elliptic to broadly obovate, 0.4–2.5 × 0.4–1.5 cm, base cuneate, veins moderately thickened, margins dentate-serrulate, apex rounded or truncate, often retuse, surfaces glabrous.
axillary or terminal, 5–20-flowered, ovoid or globose, 0.5–0.9 × 0.6 cm;
involucres absent.
axillary, 10–25-flowered, subglobose or globose, 1–1.8 × 1–1.8 cm;
involucres flattened or bowl-shaped, 4–7 mm, incised 1/2 their length, when folded, not hiding flowers except proximally, lobes 5–12, dentate-lacerate, spinulose.
1–1.5 cm.
1–2 cm.
reflexed, 0.2–0.5 mm;
bracteoles a fringe of red setae.
straight, to 1 mm;
bracteoles absent.
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.
8–10 mm;
calyx campanulate-tubular, not slit between adaxial lobes, 5–7 mm, glabrous, veins 20, tube 1.9–2.4 mm, lobes unequal, 3-fid or laciniate, often appearing 7+-lobed, orifice open;
corolla pink or pale purple, 8–9 mm, banner elliptic, 8–9 × 2–3 mm, apex retuse.
stipitate, ellipsoid, 1.5–2 mm, short beaked.
ellipsoid, 3.5–4 mm.
1, yellow or pale brown, ellipsoid, 0.9–1 mm, smooth, glossy.
2, dark brown, mottled, ovoid or reniform, 1.7–1.9 mm, smooth.
= 16, 28, 32.
Trifolium dubium
Trifolium polyodon
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.)
The taxonomic status of Trifolium polyodon, known only from Monterey County, has long been debated. W. L. Jepson (1936) considered it a variety of T. tridentatum Lindley (= T. willdenovii). The first to consider it as a variety of T. variegatum was J. S. Martin (1943), who never formally published a new combination; an invalid combination was made by M. Zohary and D. Heller (1984). D. Isely (1998) included it in his interpretation of T. variegatum as phase 5 of that species; he speculated that T. polyodon might have originated as a hybrid of T. variegatum and T. willdenovii. Molecular studies (N. W. Ellison et al. 2006) showed that T. polyodon is closely related to T. variegatum but is distinct; it also appears to be related to T. cyathiferum.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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