Trifolium dubium |
Trifolium willdenovii |
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least hop clover, lesser hop clover, lesser hop trefoil, little hop clover, shamrock, small hop-clover, suckling clover |
sand clover, thimble clover, tomcat clover, Willdenow's clover |
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Habit | Herbs annual, 20–40 cm, glabrous or sparsely hairy. | Herbs annual, 10–60 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 lanceolate or ovate, 1–2 cm, margins dentate or lacerate, apex acuminate; petiole 1–8 cm; petiolules 0.5 mm; leaflets 3, blades linear, lanceolate, or elliptic, 1–5 × 0.2–1.5 cm, base cuneate, veins fine, margins serrate, apex acute, 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, 10–50-flowered, globose or ovoid, 1–3.5 × 1–3 cm; involucres flattened or bowl-shaped, 3–9 mm, when folded, not hiding flowers except proximally, incised 1/4–1/3 their length. |
Peduncles | 1–1.5 cm. |
2–15 cm. |
Pedicels | reflexed, 0.2–0.5 mm; bracteoles a fringe of red setae. |
erect, 0.5 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. |
12–20 mm; calyx tubular-campanulate, slit between adaxial lobes, 6–9 mm, glabrous, veins 10–15, tube 3–7 mm, lobes unequal, triangular or subulate, usually 3-fid or shouldered below apex, orifice open; corolla usually white with purple spot, sometimes lavender or pink or all white, 10–18 mm, banner narrowly oblong, 12–20 × 3–4 mm, apex obtuse or retuse. |
Legumes | stipitate, ellipsoid, 1.5–2 mm, short beaked. |
ellipsoid, 3 mm. |
Seeds | 1, yellow or pale brown, ellipsoid, 0.9–1 mm, smooth, glossy. |
1 or 2, yellow, mottled, globose-ellipsoid, 1.5–2.5 mm, smooth. |
2n | = 16, 28, 32. |
= 16. |
Trifolium dubium |
Trifolium willdenovii |
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Phenology | Flowering May–Oct. | Flowering Mar–Jul. |
Habitat | Disturbed ground, fields. | Roadsides, meadows, lawns, hillsides, stream margins, open oak chaparral. |
Elevation | 0–2300 m. (0–7500 ft.) | 0–2500 m. (0–8200 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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AZ; CA; ID; OR; WA; BC; Mexico (Baja California)
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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 willdenovii was described by M. Zohary and D. Heller (1984) as one of the most variable clover species in North America. (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. involucratum, T. aciculare, T. nuttallii, T. scabrellum, T. segetum, T. tridentatum, T. tridentatum var. aciculare, T. tridentatum var. scabrellum, T. tridentatum var. segetum, T. tridentatum var. watsonii, T. trimorphum, T. watsonii |
Name authority | Sibthorp: Fl. Oxon., 231. (1794) | Sprengel: Syst. Veg. 3: 208. (1826) |
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