Trifolium dubium |
Trifolium columbinum |
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least hop clover, lesser hop clover, lesser hop trefoil, little hop clover, shamrock, small hop-clover, suckling clover |
olive clover |
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Habit | Herbs annual, 20–40 cm, glabrous or sparsely hairy. | Herbs annual, 8–30 cm, canescent. |
Stems | erect to prostrate, branched from base. |
erect, branched from base and distally, or unbranched. |
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, 0.4–1.2 cm, margins entire, ciliate, apex often purple, acuminate, setaceous; petiole 0.5–8 cm; petiolules 0.5–1 mm; leaflets 3, blades obovate or elliptic, 0.5–3 × 0.3–1.2 cm, base cuneate, veins obscure or slightly thickened, margins dentate, apex rounded or emarginate, surfaces pilose. |
Inflorescences | axillary or terminal, 5–20-flowered, ovoid or globose, 0.5–0.9 × 0.6 cm; involucres absent. |
terminal or axillary, 25–50-flowered, ovoid-ellipsoid, 1–2.5 × 1.2–2.5 cm; involucres absent. |
Peduncles | 1–1.5 cm. |
3–11 cm. |
Pedicels | reflexed, 0.2–0.5 mm; bracteoles a fringe of red setae. |
absent; bracteoles cuplike, to 0.5 mm. |
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. |
6–10 mm; calyx tubular, 8–14 mm, densely pubescent, veins 20–30, tube 1–2 mm, lobes nearly equal, appearing rigidly erect, linear-setaceous, plumose, sinuses acute, orifice open; corolla sometimes absent, red-violet, often with white tips, 4–6 mm, banner ovate-oblong, 7–8 × 2–3 mm, apex broadly rounded, apiculate. |
Legumes | stipitate, ellipsoid, 1.5–2 mm, short beaked. |
obovoid, 3–3.5 mm. |
Seeds | 1, yellow or pale brown, ellipsoid, 0.9–1 mm, smooth, glossy. |
1, yellow-brown, ellipsoid, 2–2.5 mm, smooth. |
2n | = 16, 28, 32. |
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Trifolium dubium |
Trifolium columbinum |
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Phenology | Flowering May–Oct. | Flowering Apr–May. |
Habitat | Disturbed ground, fields. | Grassy slopes, meadows, heavy adobe/clay soils, oak woodland foothills. |
Elevation | 0–2300 m. (0–7500 ft.) | 0–1400 m. (0–4600 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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CA |
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.) |
D. Isely (1998) stated that Central Valley populations of Trifolium columbinum appeared to be extinct and populations outside that region (and here recognized as the same taxon) were similar in calyx and corolla proportions. It is rather widespread in California, ranging from Humboldt County southward to Santa Barbara County, and eastward into counties ranging from Shasta southward to Inyo, Kern, and Placer counties. Trifolium albopurpureum var. olivaceum (Greene) Isely and T. columbinum var. olivaceum (Greene) Jepson are illegitimate names that pertain here (D. J. Keil 2019). (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 | T. albopurpureum var. columbinum, T. columbinum var. argillorum, T. olivaceum, T. olivaceum var. columbinum, T. olivaceum var. griseum |
Name authority | Sibthorp: Fl. Oxon., 231. (1794) | Greene: Pittonia 1: 4. (1887) |
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