Clover or trefoil are common names for plants of the genusTrifolium (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 perennialherbaceous plants. Clover can be evergreen. The leaves are trifoliate (rarely quatrefoiled, cinquefoil, or septfoil), with stipulesadnate 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 cloverTrifolium repens and red cloverTrifolium 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 acauleA. Rich.
  • Trifolium affineC. Presl
  • Trifolium africanumSer.
  • Trifolium aintabenseBoiss. & Hausskn.
  • Trifolium albopurpureumTorr. & A. Gray – rancheria clover
  • Trifolium alexandrinumL. – Egyptian clover, berseem clover
  • Trifolium alpestreL.
  • Trifolium alpinumL. – alpine clover
  • Trifolium amabileKunth
  • Trifolium ambiguumM. Bieb.
  • Trifolium amoenumGreene – showy Indian clover
  • Trifolium andersoniiA. Gray – Anderson's clover or fiveleaf clover
  • Trifolium andinumNutt. – Intermountain clover
  • Trifolium andricumLassen
  • Trifolium angulatumWaldst. & Kit.
  • Trifolium angustifoliumL.
  • Trifolium apertumBobrov
  • Trifolium argutumBanks & Sol.
  • Trifolium arvenseL. – hare's-foot clover
  • Trifolium attenuatumGreene
  • Trifolium aureumPollich – large hop trefoil
  • Trifolium baccariniiChiov.
  • Trifolium badiumSchreb.
  • Trifolium barbeyiGibelli & Belli
  • Trifolium barbigerumTorr. – bearded clover
  • Trifolium barnebyi(Isely) Dorn & Lichvar
  • Trifolium batmanicumKatzn.
  • Trifolium beckwithiiW. H. Brewer ex S. Watson – Beckwith's clover
  • Trifolium bejarienseMoric.
  • Trifolium berytheumBoiss. & Blanche
  • Trifolium bifidumA. Gray – notchleaf clover
  • Trifolium bilineatumFresen.
  • Trifolium billardiereiSpreng.
  • Trifolium bivonaeGuss.
  • Trifolium blancheanumBoiss.
  • Trifolium bocconeiSavi
  • Trifolium boissieriGuss. ex Soy.-Will. & Godr.
  • Trifolium bolanderiA. Gray
  • Trifolium brandegeeiS. Watson
  • Trifolium breweriS. Watson – forest clover
  • Trifolium brutiumTen.
  • Trifolium buckwestiorumIsely – Santa Cruz clover
  • Trifolium bullatumBoiss. & Hausskn.
  • Trifolium burchellianumSer.
  • Trifolium calcaricumJ. L. Collins & Wieboldt
  • Trifolium calocephalumFresen.
  • Trifolium campestreSchreb. – hop trefoil
  • Trifolium canescensWilld.
  • Trifolium carolinianumMichx.
  • Trifolium caucasicumTausch
  • Trifolium caudatumBoiss.
  • Trifolium cernuumBrot.
  • Trifolium cheranganienseJ. B. Gillett
  • Trifolium cherleriL.
  • Trifolium chilaloenseThulin
  • Trifolium chilenseHook. & Arn.
  • Trifolium chlorotrichumBoiss. & Balansa
  • Trifolium ciliolatumBenth. – foothill clover
  • Trifolium cinctumDC.
  • Trifolium clusiiGodr. & Gren.
  • Trifolium clypeatumL.
  • Trifolium congestumGuss.
  • Trifolium constantinopolitanumSer.
  • Trifolium cryptopodiumSteud. ex A. Rich.
  • Trifolium cyathiferumLindl. – cup clover
  • Trifolium dalmaticumVis.
  • Trifolium dasyphyllumTorr. & A. Gray
  • Trifolium dasyurumC. Presl
  • Trifolium davisiiM. Hossain
  • Trifolium decorumChiov.
  • Trifolium depauperatumDesv. – cowbag clover, balloon sack clover, or poverty clover
  • Trifolium dichotomumHook. & Arn.
  • Trifolium dichroanthoidesRech. f.
  • Trifolium dichroanthumBoiss.
  • Trifolium diffusumEhrh.
  • Trifolium dolopiumHeldr. & Hausskn. ex Gibelli & Belli
  • Trifolium douglasiiHouse
  • Trifolium dubiumSibth. – lesser hop trefoil
  • Trifolium echinatumM. Bieb.
  • Trifolium elgonenseJ. B. Gillett
  • Trifolium eriocephalumNutt. – woollyhead clover
  • Trifolium eriosphaerumBoiss.
  • Trifolium erubescensFenzl
  • Trifolium euxinumZohary
  • Trifolium eximiumStephan ex Ser.
  • Trifolium fragiferumL. – strawberry clover
  • Trifolium friscanum(S.L. Welsh) S.L. Welsh
  • Trifolium fucatumLindl. – bull clover or sour clover
  • Trifolium gemellumPourr. ex Willd.
  • Trifolium gillettianumJacq.-Fél.
  • Trifolium glanduliferumBoiss.
  • Trifolium globosumL.
  • Trifolium glomeratumL. – clustered clover or bush clover
  • Trifolium gordejevii(Kom.) Z. Wei
  • Trifolium gracilentumTorr. & A. Gray – pinpoint clover
  • Trifolium grandiflorumSchreb.
  • Trifolium gymnocarponNutt. – hollyleaf clover
  • Trifolium haussknechtiiBoiss.
  • Trifolium haydeniiPorter
  • Trifolium heldreichianum(Gibelli & Belli) Hausskn.
  • Trifolium hirtumAll. – rose clover
  • Trifolium howelliiS. Watson – canyon clover or Howell's clover
  • Trifolium hybridumL. – Alsike clover
  • Trifolium incarnatumL. – crimson clover
  • Trifolium israeliticumZohary & Katzn.
  • Trifolium isthmocarpumBrot.
  • Trifolium jokerstiiVincent & Rand. Morgan
  • Trifolium julianiBatt.
  • Trifolium kingiiS. Watson
  • Trifolium lanceolatum(J. B. Gillett) J. B. Gillett
  • Trifolium lappaceumL.
  • Trifolium latifolium(Hook.) Greene
  • Trifolium latinumSebast.
  • Trifolium leibergiiA. Nelson & J. F. Macbr. – Leiberg's clover
  • Trifolium lemmoniiS. Watson – Lemmon's clover
  • Trifolium leucanthumM. Bieb.
  • Trifolium ligusticumBalb. ex Loisel.
  • Trifolium longidentatumNábelek
  • Trifolium longipesNutt. – longstalk clover
  • Trifolium lucanicumGasp. ex Guss.
  • Trifolium lugardiiBullock
  • Trifolium lupinasterL.
  • Trifolium macilentumGreene
  • Trifolium macraeiHook. & Arn. – Chilean clover, double-head clover, or MacRae's clover
  • Trifolium macrocephalum(Pursh) Poir. – largehead clover
  • Trifolium masaienseJ. B. Gillett
  • Trifolium mattirolianumChiov.
  • Trifolium mazanderanicumRech. f.
  • Trifolium mediumL. – zigzag clover
  • Trifolium meduseumBlanche ex Boiss.
  • Trifolium meironenseZohary & Lerner
  • Trifolium michelianumSavi.
  • Trifolium micranthumViv.
  • Trifolium microcephalumPursh – smallhead clover
  • Trifolium microdonHook. & Arn. – thimble clover
  • Trifolium miegeanumMaire
  • Trifolium monanthumA. Gray – mountain carpet clover
  • Trifolium montanumL.
  • Trifolium mucronatumWilld. ex Spreng.
  • Trifolium multinerveA. Rich.
  • Trifolium mutabilePort.
  • Trifolium nanumTorr.
  • Trifolium neurophyllumGreene
  • Trifolium nigrescensViv.
  • Trifolium noricumWulfen
  • Trifolium obscurumSavi
  • Trifolium obtusiflorumHook. & Arn. – clammy clover
  • Trifolium ochroleucumHuds.
  • Trifolium oliganthumSteud. – fewflower clover
  • Trifolium ornithopodioidesL.
  • Trifolium owyheenseGilkey
  • Trifolium pachycalyxZohary
  • Trifolium palaestinumBoiss.
  • Trifolium pallescensSchreb.
  • Trifolium pallidumWaldst. & Kit.
  • Trifolium pannonicumJacq. – Hungarian clover
  • Trifolium parnassiBoiss. & Spruner
  • Trifolium parryiA. Gray
  • Trifolium patensSchreb.
  • Trifolium patulumTausch
  • Trifolium pauciflorumd'Urv.
  • Trifolium petitianumA. Rich.
  • Trifolium philistaeumZohary
  • Trifolium phitosianumN. Böhling et al.
  • Trifolium phleoidesPourr. ex Willd.
  • Trifolium physanthumHook. & Arn.
  • Trifolium physodesSteven ex M. Bieb.
  • Trifolium pichisermolliiJ. B. Gillett
  • Trifolium pignantiiBrongn. & Bory
  • Trifolium pilcziiAdamović
  • Trifolium pilulareBoiss.
  • Trifolium pinetorumGreene
  • Trifolium plebeiumBoiss.
  • Trifolium plumosumDouglas
  • Trifolium polymorphumPoir.
  • Trifolium polyodonGreene
  • Trifolium polyphyllumC. A. Mey.
  • Trifolium polystachyumFresen.
  • Trifolium praetermissumGreuter et al.
  • Trifolium pratenseL. – red clover
  • Trifolium prophetarumM. Hossain
  • Trifolium pseudostriatumBaker f.
  • Trifolium purpureumLoisel.
  • Trifolium pursegloveiJ. B. Gillett
  • Trifolium quartinianumA. Rich.
  • Trifolium radicosumBoiss. & Hohen.
  • Trifolium reflexumL. – buffalo clover
  • Trifolium repensL.shamrock (white clover)
  • Trifolium resupinatumL. – Persian clover, shaftal
  • Trifolium retusumL.
  • Trifolium riograndenseBurkart
  • Trifolium roussaeanumBoiss.
  • Trifolium rubensL.
  • Trifolium rueppellianumFresen.
  • Trifolium salmoneumMouterde
  • Trifolium saxatileAll.
  • Trifolium scabrumL.
  • Trifolium schimperiA. Rich.
  • Trifolium scutatumBoiss.
  • Trifolium sebastianiiSavi
  • Trifolium semipilosumFresen.
  • Trifolium setiferumBoiss.
  • Trifolium simenseFresen.
  • Trifolium sintenisiiFreyn
  • Trifolium siskiyouenseJ. M. Gillett
  • Trifolium somalenseTaub.
  • Trifolium spadiceumL.
  • Trifolium spananthumThulin
  • Trifolium spumosumL.
  • Trifolium squamosum (or maritimum) L. – sea clover
  • Trifolium squarrosumL.
  • Trifolium stellatumL.
  • Trifolium steudneriSchweinf.
  • Trifolium stipulaceumThunb.
  • Trifolium stoloniferumMuhl. ex A. Eaton – running buffalo clover
  • Trifolium stolziiHarms
  • Trifolium striatumL. – knotted clover
  • Trifolium strictumL.
  • Trifolium subterraneumL. – subterranean clover
  • Trifolium suffocatumL.
  • Trifolium sylvaticumGérard ex Loisel.
  • Trifolium tembenseFresen.
  • Trifolium thaliiVill.
  • Trifolium thompsoniiC. V. Morton – Thompson's clover
  • Trifolium tomentosumL.
  • Trifolium triaristatumBertero ex Colla
  • Trifolium trichocalyxA. Heller – Monterey clover
  • Trifolium trichocephalumM. Bieb.
  • Trifolium trichopterumPančić
  • Trifolium tumensSteven ex M. Bieb.
  • Trifolium ukingenseHarms
  • Trifolium uniflorumL.
  • Trifolium usambarenseTaub.
  • Trifolium variegatumNutt. – whitetip clover
  • Trifolium vaviloviiEig
  • Trifolium velebiticumDegen
  • Trifolium velenovskyiVandas
  • Trifolium vernumPhil.
  • Trifolium vesiculosumSavi
  • Trifolium vestitumD. Heller & Zohary
  • Trifolium virginicumSmall
  • Trifolium wentzelianumHarms
  • Trifolium wettsteiniiDörfl. & Hayek
  • Trifolium wigginsiiJ. M. Gillett
  • Trifolium willdenoviiSpreng. − tomcat clover
  • Trifolium wormskioldiiLehm. – cow clover