Clover

Clovers, also called trefoils, are plants of the genus Trifolium (). They are herbaceous plants growing up to tall. The leaves are usually trifoliate and the small flowers are reddish to white or yellow. Related genera with similar common names include Melilotus (sweet clover) and Medicago (burclover).

The genus consists of about 300 species in the legume family, Fabaceae. Originating in Europe, the genus has a cosmopolitan distribution. A number of wild and domestic animals consume the plants. Clovers have been cultivated by humans for over 1,000 years, valued for their nitrogen fixation, which fertilizes the soil and bolsters the productivity of rotated crops.

Some forms of the plant are culturally significant, including the shamrock, used to represent Ireland, and the four-leaf clover, associated with good luck. Specimens with other numbers of leaflets have been found, the record high of 63 being recorded in 2023.

Description They are small annual, biennial, or short-lived perennial herbaceous plants, typically growing up to tall. The leaves are trifoliate, but seldomly have more or less than three leaflets, being more rare the higher or lower the number. The stipules are adnate to the leaf-stalk. Small red, purple, white, or yellow flowers appear in heads or dense spikes. The small, few-seeded pods are enclosed in the calyx.

Other closely related genera often called clovers include Melilotus (sweet clover) and Medicago (burclover), including the species alfalfa and Calvary clover.

Taxonomy Phylogeny

The first extensive classification of Trifolium had been done by Michael Zohary and David Heller, and it was subsequently released in 1984. They divided the genus into eight sections: Lotoidea, Paramesus, Mistyllus, Vesicamridula, Chronosemium, Trifolium, Trichoecephalum, and Involucrarium, with Lotoidea placed most basally. Within this classification system, Trifolium repens falls within section Lotoidea, the largest and least heterogeneous section. Lotoidea contains species from America, Africa, and Eurasia, considered a clade because of their inflorescence shape, floral structure, and legume that protrudes from the calyx. However, these traits are not unique to the section, and are shared with many other species in other sections. Zohary and Heller argued that the presence of these traits in other sections proved the basal position of Lotoidea, because they were ancestral. Aside from considering this section basal, they did not propose relationships between other sections.

Since then, molecular data has both questioned and confirmed the proposed phylogeny from Zohary and Heller. A genus-wide molecular study has since proposed a new classification system, made up of two subgenera, Chronosemium and Trifolium. This recent reclassification further divides subgenus Trifolium into eight sections. The molecular data supports the monophyletic nature of three sections proposed by Zohary and Heller (Tripholium, Paramesus, and Trichoecepalum), but not of Lotoidea (members of this section have since been reclassified into five other sections). Other molecular studies, although smaller, support the need to reorganize Lotoidea.

Species

291 species of Trifolium are accepted:

Trifolium absconditum Trifolium acaule Steud. ex A.Rich. Trifolium affine C.Presl Trifolium acutiflorum Trifolium × adulterinum Trifolium africanum Ser. Trifolium aintabense Boiss. & Hausskn. Trifolium albopurpureum Torr. & A. Gray – rancheria clover Trifolium alexandrinum L. – Egyptian clover, berseem clover Trifolium alpestre L. – owl-head clover Trifolium alpinum L. – alpine clover Trifolium alsadami Trifolium amabile Kunth Trifolium ambiguum M. Bieb. Trifolium amoenum Greene – showy Indian clover Trifolium amphianthum 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 ankaratrense Trifolium apertum Bobrov Trifolium appendiculatum 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 barbigerum Torr. – bearded clover Trifolium barbulatum Trifolium barnebyi (Isely) Dorn & Lichvar Trifolium batmanicum Katzn. Trifolium beckwithii W.H.Brewer ex S.Watson – Beckwith's clover Trifolium bejariense Moric. Trifolium × bertrandii Trifolium berytheum Boiss. & C.I.Blanche Trifolium biebersteinii Trifolium bifidum A.Gray – notchleaf clover Trifolium bilineatum Fresen. Trifolium billardierei Spreng. Trifolium bithynicum Trifolium bivonae Guss. Trifolium blancheanum Boiss. Trifolium bobrovii Trifolium bocconei Savi Trifolium boissieri Guss. Trifolium bolanderi A.Gray Trifolium bordsilovskyi 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 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 circumdatum Kunze Trifolium clusii Godr. 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 E.Hossain Trifolium decorum Chiov. Trifolium dedeckerae 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. & Hochst. ex Gibelli & Belli Trifolium douglasii House Trifolium dubium Sibth. – lesser hop trefoil Trifolium echinatum M.Bieb. Trifolium egrissicum Trifolium elgonense J.B.Gillett Trifolium elizabethiae Trifolium eriocephalum Nutt. – woollyhead clover Trifolium eriosphaerum Boiss. Trifolium erubescens Fenzl Trifolium euxinum Zohary Trifolium eximium Stephan ex Ser. Trifolium farayense Trifolium fergan-karaeri Trifolium fontanum 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 gordeievii (Kom.) Z.Wei Trifolium gracilentum Torr. & A.Gray – pinpoint clover Trifolium grandiflorum Schreb. Trifolium gymnocarpon Nutt. – hollyleaf clover Trifolium hatschbachii Trifolium haussknechtii Boiss. Trifolium haydenii Porter Trifolium heldreichianum (Gibelli & Belli) Hausskn. Trifolium hickeyi Trifolium hirtum All. – rose clover Trifolium howellii S.Watson – canyon clover or Howell's clover Trifolium humile Trifolium hybridum L. – Alsike clover Trifolium hydrophilum Trifolium incarnatum L. – crimson clover Trifolium infamia-ponertii Trifolium israeliticum Zohary & Katzn. Trifolium isthmocarpum Brot. Trifolium jokerstii Vincent & Rand.Morgan Trifolium juliani Batt. Trifolium kentuckiense Chapel & Vincent 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. 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 C.I.Blanche ex Boiss. Trifolium meironense Zohary & Lerner Trifolium mesogitanum Trifolium michaelis Trifolium michelianum Savi Trifolium micranthum Viv. Trifolium microcephalum Pursh – smallhead clover Trifolium microdon Hook. & Arn. – thimble clover Trifolium miegeanum Maire Trifolium minutissimum Trifolium modestum Trifolium monanthum A.Gray – mountain carpet clover Trifolium montanum L. Trifolium multinerve A. Rich. Trifolium multistriatum W.D.J.Koch Trifolium mutabile Port. Trifolium nanum Torr. Trifolium nerimaniae M.Keskin Trifolium × neyrautii Trifolium nigrescens Viv. Trifolium noricum Wulfen Trifolium obscurum Savi Trifolium obtusiflorum Hook. – clammy clover Trifolium occidentale Coombe Trifolium ochroleucon Huds. - sulphur clover Trifolium oliganthum Steud. – fewflower clover Trifolium olivaceum Trifolium orbelicum Trifolium ornithopodioides L. Trifolium owyheense Gilkey Trifolium pachycalyx Zohary Trifolium palaestinum Boiss. Trifolium pallescens Schreb. Trifolium pallidum Waldst. & Kit. Trifolium palmeri Trifolium pamphylicum Trifolium pannonicum Jacq. – Hungarian clover Trifolium parnassi Boiss. & Spruner Trifolium parryi A.Gray Trifolium patens Schreb. Trifolium patulum Tausch Trifolium pauciflorum d'Urv. Trifolium × permixtum Trifolium peruvianum Vogel Trifolium philistaeum Zohary Trifolium phitosianum N.Böhling, Greuter & Raus Trifolium phleoides Pourr. ex Willd. Trifolium physanthum Hook. & Arn. Trifolium physodes Steven ex M. Bieb. Trifolium pichisermollii J.B.Gillett Trifolium pignantii Fauché. & Chaub. Trifolium pilczii Adamović Trifolium pilulare Boiss. Trifolium piorkowskii Rand.Morgan & A.L.Barber Trifolium plebeium Boiss. Trifolium plumosum Douglas ex Hook. Trifolium polymorphum Poir. Trifolium polyodon Greene Trifolium polyphyllum C.A.Mey. Trifolium polystachyum Fresen. Trifolium praetermissum Greuter, Pleger & Raus. Trifolium pratense L. – red clover Trifolium productum Trifolium prophetarum M. Hossain Trifolium pseudomedium Trifolium pseudostriatum Baker f. Trifolium pulchellum Trifolium purpureum Loisel. Trifolium purseglovei J. B. Gillett Trifolium quartinianum A. Rich. Trifolium radicosum Boiss. & Hohen. Trifolium rechingeri Trifolium reflexum L. – buffalo clover Trifolium repens L. – shamrock (white clover) Trifolium resupinatum L. – Persian clover, shaftal Trifolium retusum L. Trifolium × retyezaticum Trifolium rhizomatosum Trifolium rhombeum Trifolium riograndense Burkart Trifolium rollinsii Trifolium roussaeanum Boiss. Trifolium rubens L. Trifolium rueppellianum Fresen. Trifolium salmoneum Mouterde Trifolium sannineum Trifolium sarosiense Trifolium saxatile All. Trifolium scabrum L. Trifolium schimperi (Hochst.) A.Rich. Trifolium schneideri Trifolium × schwarzii Trifolium scutatum Boiss. Trifolium sebastiani Savi Trifolium semipilosum Fresen. Trifolium setiferum Boiss. Trifolium simense Fresen. Trifolium sintenisii Freyn Trifolium siskiyouense J.M.Gillett Trifolium somalense Taub. ex Harms Trifolium sonorense 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.