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

andrews' clover, Gray's clover

Habit Herbs annual, 20–40 cm, glabrous or sparsely hairy. Herbs annual, 10–40 cm, densely pubescent or glabrate.
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, 0.5–1.5 cm, margins toothed or lacerate, apex acute-acuminate;

petiole 1–15 cm;

petiolules 1 mm;

leaflets 3, blades elliptic, oblanceolate, or obovate, 2–2.5 × 1–1.5 cm, base cuneate, veins fine, margins dentate-serrate to crenulate, teeth shortly aristate, apex obtuse or broadly acute, surfaces pubescent or glabrate.

Inflorescences

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

involucres absent.

axillary or terminal, 5–30-flowered, subglobose or globose, 1.8–3 × 2–3 cm;

involucres bowl-shaped, 10–25 mm, lobes 6–16, sharply setaceous-toothed, sinuses shallow.

Peduncles

1–1.5 cm.

2–15 cm.

Pedicels

reflexed, 0.2–0.5 mm;

bracteoles a fringe of red setae.

straight, 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.

10–17 mm;

calyx campanulate, 6–13 mm, pubescent, veins 5, tube 3–5 mm, lobes unequal, setaceous, abaxial inconspicuously 2- or 3-fid, adaxial unbranched, segments plumose, orifice open;

corolla usually lavender or purple, sometimes purple with white tips, 8–16 mm, banner oblong, proximally inflated in fruit, distally narrowed into twisted tip, 3–5 × 10–13 mm, apex obtuse, truncate, or emarginate.

Legumes

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

stipitate, ovoid-ellipsoid, 2.5–4 mm.

Seeds

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

1 or 2, pale brown, mottled, ellipsoid to mitten-shaped, 1.6–2 mm, rugose.

2n

= 16, 28, 32.

Trifolium dubium

Trifolium grayi

Phenology Flowering May–Oct. Flowering Apr–Jun.
Habitat Disturbed ground, fields. Wet meadows, foothill slopes, pine woodlands.
Elevation 0–2300 m. (0–7500 ft.) 0–600 m. (0–2000 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
CA
[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 grayi, which ranges from San Luis Obispo County in the south to Mendocino County in the north, and eastward into Amador, Sacramento, and Tuolumne counties, has long been considered a variety of T. barbigerum and some authors claim that intermediates between the two species are encountered (J. S. Martin 1943; D. Isely 1998); others state that the two taxa are distinct (L. F. McDermott 1910; M. A Vincent and R. Morgan 1998).

Trifolium andrewsii (A. Gray) A. Heller is an illegitimate superfluous name that pertains here.

(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. 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
Synonyms Chrysaspis dubia, T. minus T. barbigerum var. andrewsii, T. barbigerum var. lilacinum, T. lilacinum
Name authority Sibthorp: Fl. Oxon., 231. (1794) Lojacono: Nuovo Giorn. Bot. Ital. 15: 189. (1883)
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