Trifolium dubium |
Trifolium trichocalyx |
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least hop clover, lesser hop clover, lesser hop trefoil, little hop clover, shamrock, small hop-clover, suckling clover |
Monterey clover |
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Habit | Herbs annual, 20–40 cm, glabrous or sparsely hairy. | Herbs annual, 5–45 cm, sparsely villous to glabrescent. |
Stems | erect to prostrate, branched from base. |
prostrate, decumbent, or 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, 0.4–1.2 cm, margins serrate-lacerate, apex acuminate; petiole 1–4 cm; petiolules 0.5 mm; leaflets 3, blades obovate, 0.5–1.5 × 0.4–1 cm, base cuneate, veins moderately prominent, margins denticulate, apex truncate, retuse, or mucronulate, surfaces glabrescent. |
Inflorescences | axillary or terminal, 5–20-flowered, ovoid or globose, 0.5–0.9 × 0.6 cm; involucres absent. |
axillary or terminal, 2–15-flowered, subglobose, 1.5–1.8 × 0.5–1.5 cm; involucres flattened or vase-shaped, 1–3 mm, when folded, not hiding flowers except proximally, incised 2/3–3/4 their length, lobes 5–15, linear-lanceolate, entire, acuminate. |
Peduncles | 1–1.5 cm. |
1.5–4 cm. |
Pedicels | reflexed, 0.2–0.5 mm; bracteoles a fringe of red setae. |
erect, 1.5 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. |
8–11 mm; calyx campanulate-tubular, not slit between adaxial lobes, 6–9 mm, usually densely pubescent, rarely sparsely so, veins 10, tube 2.5–4.5 mm, lobes unequal, lanceolate-subulate, orifice open; corolla light purple with darker purple keel petals, 6–10 mm, banner narrowly obovate, 4–5 × 1 mm, apex retuse. |
Legumes | stipitate, ellipsoid, 1.5–2 mm, short beaked. |
sessile, oblong, 5 mm. |
Seeds | 1, yellow or pale brown, ellipsoid, 0.9–1 mm, smooth, glossy. |
3–6(–9), pale brown, mottled purple, globose to mitten-shaped, 0.8–1 mm, smooth to slightly roughened, semiglossy. |
2n | = 16, 28, 32. |
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Trifolium dubium |
Trifolium trichocalyx |
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Phenology | Flowering May–Oct. | Flowering Apr–May. |
Habitat | Disturbed ground, fields. | Sandy, rich soils in open Monterey pine forests, often after fire. |
Elevation | 0–2300 m. (0–7500 ft.) | 0–50 m. (0–200 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.) |
Trifolium trichocalyx is an extremely rare species known only from Mendocino and Monterey counties. D. I. Axelrod (1982) suggested that T. trichocalyx might have originated as a hybrid between T. microcephalum and T. variegatum, but this is not supported by molecular studies (N. W. Ellison et al. 2006). It appears to be fire-adapted and appeared in large numbers shortly after a fire in 1987 (U.S. Fish and Wildlife Service 2004). (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. oliganthum var. trichocalyx |
Name authority | Sibthorp: Fl. Oxon., 231. (1794) | A. Heller: Muhlenbergia 1: 55. (1904) |
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