Trifolium vesiculosum |
Trifolium dubium |
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arrow-leaf clover |
least hop clover, lesser hop clover, lesser hop trefoil, little hop clover, shamrock, small hop-clover, suckling clover |
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Habit | Herbs annual, 15–70 cm, glabrous. | Herbs annual, 20–40 cm, glabrous or sparsely hairy. |
Stems | erect or ascending, branched. |
erect to prostrate, branched from base. |
Leaves | palmate; stipules linear-lanceolate, 1–3.5 cm, margins entire, apex subulate or setaceous; petiole 0.5–10 cm; petiolules 1 mm; leaflet 3, blades obovate to oblong, elliptic or lanceolate, 0.5–4 × 0.5–1.5 cm, base cuneate, veins prominent, thickened, margins spinulose-denticulate, apex apiculate, surfaces glabrous. |
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. |
Inflorescences | terminal or axillary, 50–100+-flowered, globose, ovoid, or oblong, 3–6 × 2–3.5 cm; involucres absent. |
axillary or terminal, 5–20-flowered, ovoid or globose, 0.5–0.9 × 0.6 cm; involucres absent. |
Peduncles | 1–12 cm. |
1–1.5 cm. |
Pedicels | absent; bracteoles lanceolate, 6–7 mm, acuminate. |
reflexed, 0.2–0.5 mm; bracteoles a fringe of red setae. |
Flowers | 12–16 mm; calyx urceolate, not bilabiate, inflated in fruit, 6–10 mm, glabrous, veins 20–36, connected by transverse veins in fruit, tube 3–5 mm, lobes reflexed, subequal, subulate, as long as tube, orifice constricted; corolla white becoming pink, 12–15 mm, banner ovate, broadly clawed, striate, 12–15 × 2–4 mm, apex acute-acuminate. |
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. |
Legumes | ellipsoid, 2.5–2.5 mm, shorter than calyx. |
stipitate, ellipsoid, 1.5–2 mm, short beaked. |
Seeds | 2 or 3, brown, ovoid, 1–1.5 mm, roughened. |
1, yellow or pale brown, ellipsoid, 0.9–1 mm, smooth, glossy. |
2n | = 16. |
= 16, 28, 32. |
Trifolium vesiculosum |
Trifolium dubium |
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Phenology | Flowering Apr–Jul. | Flowering May–Oct. |
Habitat | Fields, roadsides, forest openings. | Disturbed ground, fields. |
Elevation | 0–1000 m. (0–3300 ft.) | 0–2300 m. (0–7500 ft.) |
Distribution |
AL; AR; CA; FL; GA; LA; MA; MO; MS; OK; OR; SC; TX; VA; WA; s Europe; e Europe; w Asia [Introduced in North America]
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AK; AL; AR; AZ; CA; CT; DC; DE; FL; GA; IA; ID; IL; IN; KS; KY; LA; MA; MD; ME; MI; MN; MO; MS; MT; NC; ND; NE; NH; NJ; NM; NV; NY; OH; OK; OR; PA; RI; SC; TN; TX; VA; VT; WA; WI; WV; WY; BC; NB; NS; ON; PE; QC; SPM; c Europe; s Europe; w Asia [Introduced in North America; introduced also in s South America, e Asia (e China), n, s Africa, Pacific Islands (Hawaii, New Zealand), Australia]
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Discussion | Trifolium vesiculosum was first introduced into cultivation in the United States in 1963 and is grown in southern and western states (J. D. Miller and H. D. Wells 1985). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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.) |
Source | FNA vol. 11. | FNA vol. 11. |
Parent taxa | Fabaceae > subfam. Faboideae > Trifolium | Fabaceae > subfam. Faboideae > Trifolium |
Sibling taxa | ||
Synonyms | Chrysaspis dubia, T. minus | |
Name authority | Savi: Fl. Pis. 2: 165. (1798) — (as vessiculosum) | Sibthorp: Fl. Oxon., 231. (1794) |
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