Trifolium dubium |
Trifolium cyathiferum |
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least hop clover, lesser hop clover, lesser hop trefoil, little hop clover, shamrock, small hop-clover, suckling clover |
bowl clover, cup clover |
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Habit | Herbs annual, 20–40 cm, glabrous or sparsely hairy. | Herbs annual, 5–50 cm, glabrous. |
Stems | erect to prostrate, branched from base. |
erect, branched. |
Leaves | 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 ovate to lanceolate, 0.6–1.2 cm, margins entire, toothed, or lacerate, apex acute or aristate; petiole 1–10 cm; petiolules to 0.5 mm; leaflets 3, blades obovate, elliptic, or oblanceolate, 0.5–2.5 × 0.3–1.5 cm, base cuneate, veins prominent, green, margins finely toothed, apex rounded, blunt, or retuse, surfaces glabrous. |
Inflorescences | axillary or terminal, 5–20-flowered, ovoid or globose, 0.5–0.9 × 0.6 cm; involucres absent. |
axillary or terminal, 1–35-flowered, subglobose or ovoid, 0.5–1.8 × 0.5–2 cm; involucres broadly bowl-shaped, 4–22 mm, shallowly incised, lobes 3–15, toothed, broad, acute. |
Peduncles | 1–1.5 cm. |
1–8 cm. |
Pedicels | reflexed, 0.2–0.5 mm; bracteoles a fringe of red setae. |
straight, 0.1–0.2 mm; bracteoles absent. |
Flowers | 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. |
7–15 mm; calyx campanulate, inflated in fruit, 6–13 mm, glabrous, veins 13–20, tube 3–7 mm, lobes unequal, strongly oblique, broadly triangular, apex setaceous, adaxial unbranched, abaxial and lateral conspicuously 2- or 3-fid, segments glabrous, sometimes flattened, orifice open; corolla usually creamy white or rose to pink, sometimes whitish with pinkish tips, 6–13 mm, banner obovate or elliptic, proximally inflated in fruit, distally narrowed into twisted tip, 6–13 × 3–6 mm, apex rounded to broadly acute. |
Legumes | stipitate, ellipsoid, 1.5–2 mm, short beaked. |
ellipsoid, 2.5–3 mm. |
Seeds | 1, yellow or pale brown, ellipsoid, 0.9–1 mm, smooth, glossy. |
1 or 2, yellow-brown, ovoid, 0.4–0.6 mm, smooth. |
2n | = 16, 28, 32. |
= 16. |
Trifolium dubium |
Trifolium cyathiferum |
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Phenology | Flowering May–Oct. | Flowering Apr–Oct. |
Habitat | Disturbed ground, fields. | Wet meadows, roadsides, fields. |
Elevation | 0–2300 m. (0–7500 ft.) | 0–2700 m. (0–8900 ft.) |
Distribution |
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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AK; CA; ID; MT; NV; OR; WA; BC; YT [Introduced in Asia (China, Japan)]
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Discussion | 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 cyathiferum may be of hybrid origin; phylogenetic studies indicate it has the same trnL intron sequence as T. buckwestiorum, T. polyodon, and T. variegatum and nrDNA and combined analyses place it in a clade with other species (T. barbigerum, T. fucatum, T. jokerstii, and T. physanthum Hooker & Arnott) that have inflated fruiting corollas (N. W. Ellison et al. 2006). The single record of Trifolium cyathiferum labeled as from Utah is likely mislabeled (S. L. Welsh et al. 2008). Populations in Yukon may be introductions. (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 | Sibthorp: Fl. Oxon., 231. (1794) | Lindley: Bot. Reg. 13: sub plate 1070. (1827) |
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