Clover or trefoil are common names for plants of the genus Trifolium (Latin, tres "three" + folium "leaf"), consisting of about 300 species of plants in the leguminous pea family Fabaceae. The genus has a cosmopolitan distribution; the highest diversity is found in the temperate Northern Hemisphere, but a large number of species additionally occur in South America and Africa, including at high altitudes on mountains in the tropics. They are small annual, biennial, or short-lived perennial herbaceous plants. Clover can be evergreen. The leaves are trifoliate (rarely quatrefoiled, cinquefoil, or septfoil), with stipules adnate to the leaf-stalk, and heads or dense spikes of small red, purple, white, or yellow flowers; the small, few-seeded pods are enclosed in the calyx. Other closely related genera often called clovers include Melilotus (sweet clover) and Medicago (alfalfa or 'cavalry clover').

Cultivation

Several species of clover are extensively cultivated as fodder plants. The most widely cultivated clovers are white clover Trifolium repens and red clover Trifolium pratense. Clover, either sown alone or in mixture with ryegrass, has for a long time formed a staple crop for silaging, for several reasons: it grows freely, shooting up again after repeated mowings; it produces an abundant crop; it is palatable to and nutritious for livestock; it fixes nitrogen, reducing the need for synthetic fertilizers; it grows in a great range of soils and climates; and it is appropriate for either pasturage or green composting.

In a large number of areas, particularly on acidic soil, clover is short-lived because of a combination of insect pests, diseases and nutrient balance; this is known as "clover sickness". When crop rotations are managed so that clover doesn't recur at intervals shorter than eight years, it grows with much of its pristine vigor.

Clover sickness in more recent times might additionally be linked to pollinator decline; clovers are most efficiently pollinated by bumblebees, which have declined as a result of agricultural intensification. Honeybees can additionally pollinate clover, and beekeepers are often in heavy demand from farmers with clover pastures. Farmers reap the benefits of increased reseeding that occurs with increased bee activity, which means that future clover yields remain abundant. Beekeepers benefit from the clover bloom, as clover is one of the main nectar sources for honeybees.

Trifolium repens, white or Dutch clover, is a perennial abundant in meadows and good pastures. The flowers are white or pinkish, fitting brown and deflexed as the corolla fades. Trifolium hybridum, alsike or Swedish clover, is a perennial which was introduced early in the nineteenth century and has now become naturalised in Britain. The flowers are white or rosy, and resemble those of the last species. Trifolium medium, meadow or zigzag clover, a perennial with straggling flexuous stems and rose-purple flowers, has potential for interbreeding with T. pratense to produce perennial crop plants.

Other species are: Trifolium arvense, hare's-foot trefoil; found in fields and dry pastures, a soft hairy plant with minute white or pale pink flowers and feathery sepals; Trifolium fragiferum, strawberry clover, with globose, rose-purple heads and swollen calyxes; Trifolium campestre, hop trefoil, on dry pastures and roadsides, the heads of pale yellow flowers suggesting miniature hops; and the somewhat similar Trifolium dubium, common in pastures and roadsides, with smaller heads and small yellow flowers turning dark brown.

Symbolism

Shamrock, the traditional Irish symbol, which according to legend was coined by Saint Patrick for the Holy Trinity, is commonly associated with clover, although alternatively at times with the various species within the Oxalis genus, which are additionally trifoliate.

Clovers occasionally have four leaflets, instead of the usual three. These four-leaf clovers, like additional rarities, are considered lucky. Clovers can additionally have five, six, or more leaflets, but these are rarer. The record for most leaflets is 56, set on 10 May 2009. This beat the "21-leaf clover", a record set in June 2008 by the same discoverer, who had additionally held the prior Guinness World Record of 18.

A common idiom is "to be (or to live) in clover", meaning to live a carefree life of ease, comfort, or prosperity.

The cloverleaf interchange is named for the resemblance to the leaflets of a (four-leaf) clover when viewed from the air.

Selected species

The genus Trifolium currently has 245 recognised species:

  • Trifolium acaule A. Rich.
  • Trifolium affine C. Presl
  • Trifolium africanum Ser.
  • Trifolium aintabense Boiss. & Hausskn.
  • Trifolium albopurpureum Torr. & A. Gray – rancheria clover
  • Trifolium alexandrinum L. – Egyptian clover, berseem clover
  • Trifolium alpestre L.
  • Trifolium alpinum L. – alpine clover
  • Trifolium amabile Kunth
  • Trifolium ambiguum M. Bieb.
  • Trifolium amoenum Greene – showy Indian clover
  • Trifolium andersonii A. Gray – Anderson's clover or fiveleaf clover
  • Trifolium andinum Nutt. – Intermountain clover
  • Trifolium andricum Lassen
  • Trifolium angulatum Waldst. & Kit.
  • Trifolium angustifolium L.
  • Trifolium apertum Bobrov
  • Trifolium argutum Banks & Sol.
  • Trifolium arvense L. – hare's-foot clover
  • Trifolium attenuatum Greene
  • Trifolium aureum Pollich – large hop trefoil
  • Trifolium baccarinii Chiov.
  • Trifolium badium Schreb.
  • Trifolium barbeyi Gibelli & Belli
  • Trifolium barbigerum Torr. – bearded clover
  • Trifolium barnebyi (Isely) Dorn & Lichvar
  • Trifolium batmanicum Katzn.
  • Trifolium beckwithii W. H. Brewer ex S. Watson – Beckwith's clover
  • Trifolium bejariense Moric.
  • Trifolium berytheum Boiss. & Blanche
  • Trifolium bifidum A. Gray – notchleaf clover
  • Trifolium bilineatum Fresen.
  • Trifolium billardierei Spreng.
  • Trifolium bivonae Guss.
  • Trifolium blancheanum Boiss.
  • Trifolium bocconei Savi
  • Trifolium boissieri Guss. ex Soy.-Will. & Godr.
  • Trifolium bolanderi A. Gray
  • Trifolium brandegeei S. Watson
  • Trifolium breweri S. Watson – forest clover
  • Trifolium brutium Ten.
  • Trifolium buckwestiorum Isely – Santa Cruz clover
  • Trifolium bullatum Boiss. & Hausskn.
  • Trifolium burchellianum Ser.
  • Trifolium calcaricum J. L. Collins & Wieboldt
  • Trifolium calocephalum Fresen.
  • Trifolium campestre Schreb. – hop trefoil
  • Trifolium canescens Willd.
  • Trifolium carolinianum Michx.
  • Trifolium caucasicum Tausch
  • Trifolium caudatum Boiss.
  • Trifolium cernuum Brot.
  • Trifolium cheranganiense J. B. Gillett
  • Trifolium cherleri L.
  • Trifolium chilaloense Thulin
  • Trifolium chilense Hook. & Arn.
  • Trifolium chlorotrichum Boiss. & Balansa
  • Trifolium ciliolatum Benth. – foothill clover
  • Trifolium cinctum DC.
  • Trifolium clusii Godr. & Gren.
  • Trifolium clypeatum L.
  • Trifolium congestum Guss.
  • Trifolium constantinopolitanum Ser.
  • Trifolium cryptopodium Steud. ex A. Rich.
  • Trifolium cyathiferum Lindl. – cup clover
  • Trifolium dalmaticum Vis.
  • Trifolium dasyphyllum Torr. & A. Gray
  • Trifolium dasyurum C. Presl
  • Trifolium davisii M. Hossain
  • Trifolium decorum Chiov.
  • Trifolium depauperatum Desv. – cowbag clover, balloon sack clover, or poverty clover
  • Trifolium dichotomum Hook. & Arn.
  • Trifolium dichroanthoides Rech. f.
  • Trifolium dichroanthum Boiss.
  • Trifolium diffusum Ehrh.
  • Trifolium dolopium Heldr. & Hausskn. ex Gibelli & Belli
  • Trifolium douglasii House
  • Trifolium dubium Sibth. – lesser hop trefoil
  • Trifolium echinatum M. Bieb.
  • Trifolium elgonense J. B. Gillett
  • Trifolium eriocephalum Nutt. – woollyhead clover
  • Trifolium eriosphaerum Boiss.
  • Trifolium erubescens Fenzl
  • Trifolium euxinum Zohary
  • Trifolium eximium Stephan ex Ser.
  • Trifolium fragiferum L. – strawberry clover
  • Trifolium friscanum (S.L. Welsh) S.L. Welsh
  • Trifolium fucatum Lindl. – bull clover or sour clover
  • Trifolium gemellum Pourr. ex Willd.
  • Trifolium gillettianum Jacq.-Fél.
  • Trifolium glanduliferum Boiss.
  • Trifolium globosum L.
  • Trifolium glomeratum L. – clustered clover or bush clover
  • Trifolium gordejevii (Kom.) Z. Wei
  • Trifolium gracilentum Torr. & A. Gray – pinpoint clover
  • Trifolium grandiflorum Schreb.
  • Trifolium gymnocarpon Nutt. – hollyleaf clover
  • Trifolium haussknechtii Boiss.
  • Trifolium haydenii Porter
  • Trifolium heldreichianum (Gibelli & Belli) Hausskn.
  • Trifolium hirtum All. – rose clover
  • Trifolium howellii S. Watson – canyon clover or Howell's clover
  • Trifolium hybridum L. – Alsike clover
  • Trifolium incarnatum L. – crimson clover
  • Trifolium israeliticum Zohary & Katzn.
  • Trifolium isthmocarpum Brot.
  • Trifolium jokerstii Vincent & Rand. Morgan
  • Trifolium juliani Batt.
  • Trifolium kingii S. Watson
  • Trifolium lanceolatum (J. B. Gillett) J. B. Gillett
  • Trifolium lappaceum L.
  • Trifolium latifolium (Hook.) Greene
  • Trifolium latinum Sebast.
  • Trifolium leibergii A. Nelson & J. F. Macbr. – Leiberg's clover
  • Trifolium lemmonii S. Watson – Lemmon's clover
  • Trifolium leucanthum M. Bieb.
  • Trifolium ligusticum Balb. ex Loisel.
  • Trifolium longidentatum Nábelek
  • Trifolium longipes Nutt. – longstalk clover
  • Trifolium lucanicum Gasp. ex Guss.
  • Trifolium lugardii Bullock
  • Trifolium lupinaster L.
  • Trifolium macilentum Greene
  • Trifolium macraei Hook. & Arn. – Chilean clover, double-head clover, or MacRae's clover
  • Trifolium macrocephalum (Pursh) Poir. – largehead clover
  • Trifolium masaiense J. B. Gillett
  • Trifolium mattirolianum Chiov.
  • Trifolium mazanderanicum Rech. f.
  • Trifolium medium L. – zigzag clover
  • Trifolium meduseum Blanche ex Boiss.
  • Trifolium meironense Zohary & Lerner
  • Trifolium michelianum Savi.
  • Trifolium micranthum Viv.
  • Trifolium microcephalum Pursh – smallhead clover
  • Trifolium microdon Hook. & Arn. – thimble clover
  • Trifolium miegeanum Maire
  • Trifolium monanthum A. Gray – mountain carpet clover
  • Trifolium montanum L.
  • Trifolium mucronatum Willd. ex Spreng.
  • Trifolium multinerve A. Rich.
  • Trifolium mutabile Port.
  • Trifolium nanum Torr.
  • Trifolium neurophyllum Greene
  • Trifolium nigrescens Viv.
  • Trifolium noricum Wulfen
  • Trifolium obscurum Savi
  • Trifolium obtusiflorum Hook. & Arn. – clammy clover
  • Trifolium ochroleucum Huds.
  • Trifolium oliganthum Steud. – fewflower clover
  • Trifolium ornithopodioides L.
  • Trifolium owyheense Gilkey
  • Trifolium pachycalyx Zohary
  • Trifolium palaestinum Boiss.
  • Trifolium pallescens Schreb.
  • Trifolium pallidum Waldst. & Kit.
  • Trifolium pannonicum Jacq. – Hungarian clover
  • Trifolium parnassi Boiss. & Spruner
  • Trifolium parryi A. Gray
  • Trifolium patens Schreb.
  • Trifolium patulum Tausch
  • Trifolium pauciflorum d'Urv.
  • Trifolium petitianum A. Rich.
  • Trifolium philistaeum Zohary
  • Trifolium phitosianum N. Böhling et al.
  • Trifolium phleoides Pourr. ex Willd.
  • Trifolium physanthum Hook. & Arn.
  • Trifolium physodes Steven ex M. Bieb.
  • Trifolium pichisermollii J. B. Gillett
  • Trifolium pignantii Brongn. & Bory
  • Trifolium pilczii Adamović
  • Trifolium pilulare Boiss.
  • Trifolium pinetorum Greene
  • Trifolium plebeium Boiss.
  • Trifolium plumosum Douglas
  • Trifolium polymorphum Poir.
  • Trifolium polyodon Greene
  • Trifolium polyphyllum C. A. Mey.
  • Trifolium polystachyum Fresen.
  • Trifolium praetermissum Greuter et al.
  • Trifolium pratense L. – red clover
  • Trifolium prophetarum M. Hossain
  • Trifolium pseudostriatum Baker f.
  • Trifolium purpureum Loisel.
  • Trifolium purseglovei J. B. Gillett
  • Trifolium quartinianum A. Rich.
  • Trifolium radicosum Boiss. & Hohen.
  • Trifolium reflexum L. – buffalo clover
  • Trifolium repens L.shamrock (white clover)
  • Trifolium resupinatum L. – Persian clover, shaftal
  • Trifolium retusum L.
  • Trifolium riograndense Burkart
  • Trifolium roussaeanum Boiss.
  • Trifolium rubens L.
  • Trifolium rueppellianum Fresen.
  • Trifolium salmoneum Mouterde
  • Trifolium saxatile All.
  • Trifolium scabrum L.
  • Trifolium schimperi A. Rich.
  • Trifolium scutatum Boiss.
  • Trifolium sebastianii Savi
  • Trifolium semipilosum Fresen.
  • Trifolium setiferum Boiss.
  • Trifolium simense Fresen.
  • Trifolium sintenisii Freyn
  • Trifolium siskiyouense J. M. Gillett
  • Trifolium somalense Taub.
  • Trifolium spadiceum L.
  • Trifolium spananthum Thulin
  • Trifolium spumosum L.
  • Trifolium squamosum (or maritimum) L. – sea clover
  • Trifolium squarrosum L.
  • Trifolium stellatum L.
  • Trifolium steudneri Schweinf.
  • Trifolium stipulaceum Thunb.
  • Trifolium stoloniferum Muhl. ex A. Eaton – running buffalo clover
  • Trifolium stolzii Harms
  • Trifolium striatum L. – knotted clover
  • Trifolium strictum L.
  • Trifolium subterraneum L. – subterranean clover
  • Trifolium suffocatum L.
  • Trifolium sylvaticum Gérard ex Loisel.
  • Trifolium tembense Fresen.
  • Trifolium thalii Vill.
  • Trifolium thompsonii C. V. Morton – Thompson's clover
  • Trifolium tomentosum L.
  • Trifolium triaristatum Bertero ex Colla
  • Trifolium trichocalyx A. Heller – Monterey clover
  • Trifolium trichocephalum M. Bieb.
  • Trifolium trichopterum Pančić
  • Trifolium tumens Steven ex M. Bieb.
  • Trifolium ukingense Harms
  • Trifolium uniflorum L.
  • Trifolium usambarense Taub.
  • Trifolium variegatum Nutt. – whitetip clover
  • Trifolium vavilovii Eig
  • Trifolium velebiticum Degen
  • Trifolium velenovskyi Vandas
  • Trifolium vernum Phil.
  • Trifolium vesiculosum Savi
  • Trifolium vestitum D. Heller & Zohary
  • Trifolium virginicum Small
  • Trifolium wentzelianum Harms
  • Trifolium wettsteinii Dörfl. & Hayek
  • Trifolium wigginsii J. M. Gillett
  • Trifolium willdenovii Spreng. − tomcat clover
  • Trifolium wormskioldii Lehm. – cow clover