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least hop clover, lesser hop clover, lesser hop trefoil, little hop clover, shamrock, small hop-clover, suckling clover

arrow-leaf clover

Habit Herbs annual, 20–40 cm, glabrous or sparsely hairy. Herbs annual, 15–70 cm, glabrous.
Stems

erect to prostrate, branched from base.

erect or ascending, 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 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.

Inflorescences

axillary or terminal, 5–20-flowered, ovoid or globose, 0.5–0.9 × 0.6 cm;

involucres absent.

terminal or axillary, 50–100+-flowered, globose, ovoid, or oblong, 3–6 × 2–3.5 cm;

involucres absent.

Peduncles

1–1.5 cm.

1–12 cm.

Pedicels

reflexed, 0.2–0.5 mm;

bracteoles a fringe of red setae.

absent;

bracteoles lanceolate, 6–7 mm, acuminate.

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.

12–16 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.

Legumes

stipitate, ellipsoid, 1.5–2 mm, short beaked.

ellipsoid, 2.5–2.5 mm, shorter than calyx.

Seeds

1, yellow or pale brown, ellipsoid, 0.9–1 mm, smooth, glossy.

2 or 3, brown, ovoid, 1–1.5 mm, roughened.

2n

= 16, 28, 32.

= 16.

Trifolium dubium

Trifolium vesiculosum

Phenology Flowering May–Oct. Flowering Apr–Jul.
Habitat Disturbed ground, fields. Fields, roadsides, forest openings.
Elevation 0–2300 m. (0–7500 ft.) 0–1000 m. (0–3300 ft.)
Distribution
from FNA
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]
[WildflowerSearch map]
[BONAP county map]
from FNA
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]
[WildflowerSearch map]
[BONAP county map]
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 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.)

Source FNA vol. 11. FNA vol. 11.
Parent taxa Fabaceae > subfam. Faboideae > Trifolium Fabaceae > subfam. Faboideae > Trifolium
Sibling taxa
T. albopurpureum, T. alexandrinum, T. amoenum, T. amphianthum, T. andersonii, T. andinum, T. angustifolium, T. appendiculatum, T. arvense, T. attenuatum, T. aureum, T. barbigerum, T. barnebyi, T. beckwithii, T. bejariense, T. bifidum, T. bolanderi, T. brandegeei, T. breweri, T. buckwestiorum, T. calcaricum, T. campestre, T. carolinianum, T. cernuum, T. ciliolatum, T. columbinum, T. cyathiferum, T. dasyphyllum, T. dedeckerae, T. depauperatum, T. dichotomum, T. douglasii, T. echinatum, T. eriocephalum, T. fragiferum, T. friscanum, T. fucatum, T. glomeratum, T. gracilentum, T. grayi, T. gymnocarpon, T. haydenii, T. hirtum, T. howellii, T. hybridum, T. hydrophilum, T. incarnatum, T. jokerstii, T. kentuckiense, T. kingii, T. lappaceum, T. latifolium, T. leibergii, T. lemmonii, T. longipes, T. lupinaster, T. macilentum, T. macraei, T. macrocephalum, T. medium, T. microcephalum, T. microdon, T. monanthum, T. mucronatum, T. nanum, T. nigrescens, T. obtusiflorum, T. oliganthum, T. ornithopodioides, T. owyheense, T. palmeri, T. parryi, T. pinetorum, T. piorkowskii, T. plumosum, T. polyodon, T. pratense, T. productum, T. reflexum, T. repens, T. resupinatum, T. retusum, T. rollinsii, T. siskiyouense, T. sonorense, T. stoloniferum, T. striatum, T. subterraneum, T. suffocatum, T. thompsonii, T. tomentosum, T. trichocalyx, T. variegatum, T. vesiculosum, T. virginicum, T. willdenovii, T. wormskioldii
T. albopurpureum, T. alexandrinum, T. amoenum, T. amphianthum, T. andersonii, T. andinum, T. angustifolium, T. appendiculatum, T. arvense, T. attenuatum, T. aureum, T. barbigerum, T. barnebyi, T. beckwithii, T. bejariense, T. bifidum, T. bolanderi, T. brandegeei, T. breweri, T. buckwestiorum, T. calcaricum, T. campestre, T. carolinianum, T. cernuum, T. ciliolatum, T. columbinum, T. cyathiferum, T. dasyphyllum, T. dedeckerae, T. depauperatum, T. dichotomum, T. douglasii, T. dubium, T. echinatum, T. eriocephalum, T. fragiferum, T. friscanum, T. fucatum, T. glomeratum, T. gracilentum, T. grayi, T. gymnocarpon, T. haydenii, T. hirtum, T. howellii, T. hybridum, T. hydrophilum, T. incarnatum, T. jokerstii, T. kentuckiense, T. kingii, T. lappaceum, T. latifolium, T. leibergii, T. lemmonii, T. longipes, T. lupinaster, T. macilentum, T. macraei, T. macrocephalum, T. medium, T. microcephalum, T. microdon, T. monanthum, T. mucronatum, T. nanum, T. nigrescens, T. obtusiflorum, T. oliganthum, T. ornithopodioides, T. owyheense, T. palmeri, T. parryi, T. pinetorum, T. piorkowskii, T. plumosum, T. polyodon, T. pratense, T. productum, T. reflexum, T. repens, T. resupinatum, T. retusum, T. rollinsii, T. siskiyouense, T. sonorense, T. stoloniferum, T. striatum, T. subterraneum, T. suffocatum, T. thompsonii, T. tomentosum, T. trichocalyx, T. variegatum, T. virginicum, T. willdenovii, T. wormskioldii
Synonyms Chrysaspis dubia, T. minus
Name authority Sibthorp: Fl. Oxon., 231. (1794) Savi: Fl. Pis. 2: 165. (1798) — (as vessiculosum)
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