Invasive Species Compendium

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Datasheet

Melilotus albus
(honey clover)

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Datasheet

Melilotus albus (honey clover)

Summary

  • Last modified
  • 27 September 2018
  • Datasheet Type(s)
  • Invasive Species
  • Host Plant
  • Preferred Scientific Name
  • Melilotus albus
  • Preferred Common Name
  • honey clover
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Dicotyledonae
  • Summary of Invasiveness
  • M. albus is a legume native from south-western Europe to China, the Middle East and north-eastern Africa. It has been introduced to northern Europe, North and South America, Australasia and southern Africa, oft...

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    OX10 8DE
    UK
    compend@cabi.org
  • Distribution map More information

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Pictures

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PictureTitleCaptionCopyright
Melilotus albus (white melilot, honey clover); large flowering plant on gravel
TitleHabit
CaptionMelilotus albus (white melilot, honey clover); large flowering plant on gravel
Copyright©Trevor James/Hamilton, New Zealand
Melilotus albus (white melilot, honey clover); large flowering plant on gravel
HabitMelilotus albus (white melilot, honey clover); large flowering plant on gravel©Trevor James/Hamilton, New Zealand
Melilotus albus (white melilot, honey clover); detail of flowering plant
TitleHabit
CaptionMelilotus albus (white melilot, honey clover); detail of flowering plant
Copyright©Trevor James/Hamilton, New Zealand
Melilotus albus (white melilot, honey clover); detail of flowering plant
HabitMelilotus albus (white melilot, honey clover); detail of flowering plant©Trevor James/Hamilton, New Zealand
Melilotus albus (whte melilot, honey clover); young flowers and leaves
TitleYoung flowers and leaves
CaptionMelilotus albus (whte melilot, honey clover); young flowers and leaves
Copyright©Trevor James/Hamilton, New Zealand
Melilotus albus (whte melilot, honey clover); young flowers and leaves
Young flowers and leavesMelilotus albus (whte melilot, honey clover); young flowers and leaves©Trevor James/Hamilton, New Zealand
Melilotus albus (whte melilot, honey clover); young flowers and leaves
TitleFlowers and leaves
CaptionMelilotus albus (whte melilot, honey clover); young flowers and leaves
Copyright©Trevor James/Hamilton, New Zealand
Melilotus albus (whte melilot, honey clover); young flowers and leaves
Flowers and leavesMelilotus albus (whte melilot, honey clover); young flowers and leaves©Trevor James/Hamilton, New Zealand
Melilotus albus (whte melilot, honey clover); flower spike
TitleFlower spike
CaptionMelilotus albus (whte melilot, honey clover); flower spike
Copyright©Trevor James/Hamilton, New Zealand
Melilotus albus (whte melilot, honey clover); flower spike
Flower spikeMelilotus albus (whte melilot, honey clover); flower spike©Trevor James/Hamilton, New Zealand
Melilotus albus (whte melilot, honey clover); close-up of flower spike
TitleFlower spike
CaptionMelilotus albus (whte melilot, honey clover); close-up of flower spike
Copyright©Trevor James/Hamilton, New Zealand
Melilotus albus (whte melilot, honey clover); close-up of flower spike
Flower spikeMelilotus albus (whte melilot, honey clover); close-up of flower spike©Trevor James/Hamilton, New Zealand

Identity

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Preferred Scientific Name

  • Melilotus albus Medik.

Preferred Common Name

  • honey clover

International Common Names

  • English: bokhara clover (Australia); sweet clover; white melilot; white melilot (UK); white sweet clover (USA)
  • Spanish: alfa-rusa (Argentina); meliloto blanco; trebol blanco; trebol de olor blanco (Bolivia); trebol de Santa Maria (Nicaragua)
  • French: melilot blanc; trèfle de Bokhara
  • Portuguese: meliloto-branco

Local Common Names

  • : handaquq; nafal
  • Armenia: isharvuit spitak
  • Azerbaijan: ag kheshenbul
  • Brazil: trevo-doce-branco
  • China: bai hua cao mu xi
  • Estonia: valge mesikas
  • Finland: valkomesikka
  • Germany: Bokharaklee; Bokharaklee; Bucharaklee; Honigklee; Steinklee, Weisser; weisser Steinklee
  • Italy: meliloto bianco; meliloto bianco; meliloto bianco; trifoglio di Bokhara; trilobo bianco; vetturina bianca
  • Japan: shirobana-shinagawa-hagi
  • Korea, Republic of: huinje ondongs sari
  • Latvia: baltais amolins
  • Lithuania: baltaziedis barkunas
  • Moldova: sulchine albe
  • Mongolia: gavir tzetzeg; zagaan khoshoon
  • Netherlands: witte honingklaver
  • Norway: hvitsteinklover
  • Poland: nostrzyk bialy
  • Portugal: meliloto branco; meliloto-branco
  • Russian Federation: donnik belyi; sulfina alba; urun donnik (Yakut)
  • Spain: meliloto blanco; meliloto-blanco
  • Sweden: vit sotvappling; vit sotvappling; vitmelot
  • Turkmenistan: eshekyorunzha
  • Ukraine: burkun bilyi

EPPO code

  • MEUAL (Melilotus alba)

Summary of Invasiveness

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M. albus is a legume native from south-western Europe to China, the Middle East and north-eastern Africa. It has been introduced to northern Europe, North and South America, Australasia and southern Africa, often as a potential fodder crop. M. albus has typical weedy attributes such as prolific seed production, persistence and presence along roadsides and railways (Turkington et al., 1978), and as a result can negatively impact ecosystem services, wildlife habitats, and agriculture (Gucker, 2009). Although M. albus can be a problematic invasive species it is also important in many places as a fodder crop, a honey producer, soil stabiliser and a useful species for land reclamation.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Dicotyledonae
  •                     Order: Fabales
  •                         Family: Fabaceae
  •                             Subfamily: Papilionoideae
  •                                 Genus: Melilotus
  •                                     Species: Melilotus albus

Notes on Taxonomy and Nomenclature

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M. albus can either be annual or biennial. The annual form has been named M. albus var. annuus, but this is not accepted (ITIS, 2013).

Description

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From Turkington et al. (1978), in turn modified from Stevenson (1969):

Plants have a strong tap root, a crown which produces 1 to 10 upright stems, and trifoliate leaves with the terminal leaflet stalked.

Stem 0.3-2.6 m high, upright, coarse or fine, grooved or channelled, usually pubescent or pilose near the tip. Leaflets of the trifoliate lower leaves broadly ovate, obovate or rhomboidal, rounded or truncate at the tip, irregularly dentate, 1.5-5 cm long; those of the upper leaves oblong-lanceolate, usually rounded or truncate at the tip, dentate or almost entire. Stipules 7-10 mm long, entire, narrowly cuneate, those of the lower leaves with one or two teeth near the broadened base. Each raceme 40-80, rarely 120 flowered, elongated at maturity, 8-15 cm long or occasionally up to 28 cm in some annual varieties. Pedicels 1.5-2 mm long. Flowers-white, 4-6 mm long, single, 10 stamens, 2 ovules in ovary, style and stigma hidden inside a pair of keel petals which are more or less fused along the outer margin to form the keel. Calyx 2-2.5 mm long, teeth as long as the tube, rarely shorter, triangular-lanceolate. Wings and standard more or less equal and longer than the keel. Pod 3-4 mm long, 2-2.5 mm broad, 1.5-2 mm thick, obliquely ovate, reticulately nerved, black, dark grey or tawny, tip obtuse, base of style persisting. Pods usually have 1 seed, rarely 2 or 3. Seeds oval 2-2.5 mm long, 1.5 mm broad, yellow or rarely greenish-yellow; endosperm present, two-layered and completely enclosing the embryo.

Weaver (1920, cited in Gucker, 2009) observed first year taproots over 1.2 m deep and second year ones up to 1.7 m deep.

Plant Type

Top of page Annual
Biennial
Broadleaved
Herbaceous
Seed propagated

Distribution

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M. albus is native to much of Asia and southern Europe, from France and Spain to Kazakhstan and Myanmar, and also north-east Africa (USDA-ARS, 2014). It has been introduced to many parts of Europe outside its native range, as well as to North and South America, Australasia and southern Africa, often as a crop or potential crop (Turkington et al., 1978). In the USA, the species is considered most common in the upper Midwest and Great Plains regions, including Kentucky, Nebraska, Tennessee and Wisconsin (Gucker, 2009; USDA-NRCS, 2013).

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Asia

AfghanistanPresentNativeUSDA-ARS, 2013
ArmeniaPresentNativeUSDA-ARS, 2013
AzerbaijanPresentNativeUSDA-ARS, 2013
BangladeshPresentILDIS, 2013
BhutanPresentNativeUSDA-ARS, 2013
ChinaPresentNativeUSDA-ARS, 2013
-BeijingPresentNativeWang et al., 2011Present in all the districts and counties of Beijing
-ShanghaiPresentIntroducedHsu, 2010
-TibetPresentIntroducedILDIS, 2013
Georgia (Republic of)PresentNativeUSDA-ARS, 2013
IndiaPresentUSDA-ARS, 2013
-Indian PunjabUnconfirmed recordCAB Abstracts
-Jammu and KashmirUnconfirmed recordCAB Abstracts; Kaul, 1986
-Madhya PradeshPresent
-OdishaPresent
-Uttar PradeshUnconfirmed recordCAB Abstracts; Khanna, 2009
IranPresentNativeUSDA-ARS, 2013
IraqPresentNativeUSDA-ARS, 2013
IsraelPresentNativeUSDA-ARS, 2013
JapanPresentIntroducedPIER, 2013
JordanPresentNativeUSDA-ARS, 2013
KazakhstanPresentNativeUSDA-ARS, 2013
Korea, Republic ofPresentNativeKil et al., 2004
KuwaitPresentMathew et al., 2012
KyrgyzstanPresentNativeUSDA-ARS, 2013
LebanonPresentNativeUSDA-ARS, 2013
MongoliaPresentILDIS, 2013
MyanmarPresentNativeUSDA-ARS, 2013
NepalPresentILDIS, 2013
PakistanPresentNativeUSDA-ARS, 2013
QatarPresentILDIS, 2013
Saudi ArabiaPresentNativeUSDA-ARS, 2013
SyriaPresentILDIS, 2013
TajikistanPresentNativeUSDA-ARS, 2013
TurkeyPresentNativeUSDA-ARS, 2013
TurkmenistanPresentNativeUSDA-ARS, 2013
United Arab EmiratesPresentNativeUSDA-ARS, 2013
UzbekistanPresentNativeUSDA-ARS, 2013
YemenPresentNativeUSDA-ARS, 2013

Africa

AlgeriaPresentIntroducedILDIS, 2013
EgyptPresentNativeUSDA-ARS, 2013
EthiopiaPresentIntroducedILDIS, 2013
KenyaPresentIntroducedILDIS, 2013
LesothoPresentIntroducedILDIS, 2013
LibyaPresentNativeUSDA-ARS, 2013
MauritiusPresentIntroducedPIER, 2013
MozambiquePresent only in captivity/cultivationIntroducedHyde et al., 2013
RéunionPresentILDIS, 2013
Rodriguez IslandPresentIntroducedILDIS, 2013
South AfricaPresentIntroducedUSDA-ARS, 2013
Spain
-Canary IslandsPresentIntroduced
TanzaniaPresentIntroduced
ZimbabwePresentIntroducedILDIS, 2013

North America

CanadaPresent
-AlbertaUnconfirmed record
-British ColumbiaPresentIntroduced Invasive USDA-NRCS, 2013
-ManitobaPresentIntroduced Invasive USDA-NRCS, 2013
-New BrunswickPresentIntroduced Invasive USDA-NRCS, 2013
-Newfoundland and LabradorPresentIntroduced Invasive USDA-NRCS, 2013
-Northwest TerritoriesPresentIntroduced Invasive USDA-NRCS, 2013
-Nova ScotiaPresentIntroduced Invasive USDA-NRCS, 2013
-NunavutPresentIntroduced Invasive USDA-NRCS, 2013
-OntarioPresentIntroduced Invasive USDA-NRCS, 2013
-Prince Edward IslandPresentIntroduced Invasive USDA-NRCS, 2013
-QuebecPresentIntroduced Invasive USDA-NRCS, 2013
-SaskatchewanPresentUSDA-NRCS, 2013
-Yukon TerritoryPresentIntroduced Invasive USDA-NRCS, 2013
GreenlandPresentIntroduced Invasive USDA-NRCS, 2013
MexicoPresentIntroduced Invasive Weeds of Mexico, 2013
Saint Pierre and MiquelonPresentIntroduced Invasive USDA-NRCS, 2013
USAUnconfirmed record
-AlabamaPresentIntroduced Invasive USDA-NRCS, 2013
-AlaskaPresentIntroduced Invasive USDA-NRCS, 2013
-ArizonaPresentIntroduced Invasive USDA-NRCS, 2013
-ArkansasPresentIntroduced Invasive USDA-NRCS, 2013
-CaliforniaPresentIntroduced Invasive USDA-NRCS, 2013
-ColoradoPresentIntroduced Invasive USDA-NRCS, 2013
-ConnecticutPresentIntroduced Invasive USDA-NRCS, 2013
-DelawarePresentIntroduced Invasive USDA-NRCS, 2013
-District of ColumbiaPresentIntroduced Invasive USDA-NRCS, 2013
-FloridaPresentIntroduced Invasive USDA-NRCS, 2013
-GeorgiaPresentIntroduced Invasive USDA-NRCS, 2013
-HawaiiPresentIntroduced Invasive USDA-NRCS, 2013
-IdahoPresentIntroduced Invasive USDA-NRCS, 2013
-IllinoisPresentIntroduced Invasive USDA-NRCS, 2013
-IndianaPresentIntroduced Invasive USDA-NRCS, 2013
-IowaPresentIntroduced Invasive USDA-NRCS, 2013
-KansasPresentIntroduced Invasive USDA-NRCS, 2013
-KentuckyPresentIntroduced Invasive USDA-NRCS, 2013
-LouisianaPresentIntroduced Invasive USDA-NRCS, 2013
-MainePresentIntroduced Invasive USDA-NRCS, 2013
-MarylandPresentIntroduced Invasive USDA-NRCS, 2013
-MassachusettsPresentIntroduced Invasive USDA-NRCS, 2013
-MichiganPresentIntroduced Invasive USDA-NRCS, 2013
-MinnesotaPresentIntroduced Invasive USDA-NRCS, 2013
-MississippiPresentIntroduced Invasive USDA-NRCS, 2013
-MissouriPresentIntroduced Invasive USDA-NRCS, 2013
-MontanaPresentIntroduced Invasive USDA-NRCS, 2013
-NevadaPresentIntroduced Invasive USDA-NRCS, 2013
-New HampshirePresentIntroduced Invasive USDA-NRCS, 2013
-New JerseyPresentIntroduced Invasive USDA-NRCS, 2013
-New MexicoPresentIntroduced Invasive USDA-NRCS, 2013
-New YorkUnconfirmed recordUSDA-NRCS, 2013
-North CarolinaPresentIntroduced Invasive USDA-NRCS, 2013
-North DakotaPresentIntroduced Invasive USDA-NRCS, 2013
-OhioPresentIntroduced Invasive USDA-NRCS, 2013
-OklahomaPresentIntroduced Invasive USDA-NRCS, 2013
-OregonPresentIntroduced Invasive USDA-NRCS, 2013
-PennsylvaniaPresentIntroduced Invasive USDA-NRCS, 2013
-Rhode IslandPresentIntroduced Invasive USDA-NRCS, 2013
-South CarolinaPresentIntroduced Invasive USDA-NRCS, 2013
-South DakotaPresentIntroduced Invasive USDA-NRCS, 2013
-TennesseePresentIntroduced Invasive USDA-NRCS, 2013
-TexasPresentIntroduced Invasive USDA-NRCS, 2013
-UtahPresentIntroduced Invasive USDA-NRCS, 2013
-VermontPresentIntroduced Invasive USDA-NRCS, 2013
-VirginiaPresentIntroduced Invasive USDA-NRCS, 2013
-WashingtonUnconfirmed recordUSDA-NRCS, 2013
-West VirginiaPresentIntroduced Invasive USDA-NRCS, 2013
-WisconsinPresentIntroduced Invasive USDA-NRCS, 2013
-WyomingPresentIntroduced Invasive USDA-NRCS, 2013

Central America and Caribbean

BahamasPresentIntroducedILDIS, 2013
BelizePresentIntroduced Not invasive BERDS, 2006
Dominican RepublicPresentIntroducedILDIS, 2013
HaitiPresentIntroducedILDIS, 2013
JamaicaPresentIntroducedILDIS, 2013
Puerto RicoPresentIntroducedILDIS, 2013

South America

ArgentinaPresent only in captivity/cultivationIntroducedEvans, 2001
BrazilPresentIntroducedSchneider, 2007
-Rio Grande do SulPresentIntroducedSchneider, 2007
ChilePresentIntroducedPIER, 2013
ColombiaPresentIntroducedCardenas and Coulston, 1967
EcuadorPresentIntroducedJørgensen and León-Yànez, 1999
PeruPresentIntroducedRandall, 2012
UruguayPresentIntroducedIABIN, 2008
VenezuelaPresentIntroducedCardenas and Coulston, 1967

Europe

AlbaniaPresentNativeUSDA-ARS, 2013
AustriaPresentNativeUSDA-ARS, 2013
BelarusPresentNative
BelgiumPresentIntroducedNear cities, still increasing
BulgariaPresentIntroduced
CyprusPresentNativeUSDA-ARS, 2013
Czech RepublicPresentDAISIE, 2008
Czechoslovakia (former)PresentNativeUSDA-ARS, 2013
DenmarkPresentIntroducedDAISIE, 2008
EstoniaPresentNativeUSDA-ARS, 2013
FinlandPresentDAISIE, 2008
FrancePresentNativeUSDA-ARS, 2013
-CorsicaPresentIntroducedDAISIE, 2008
GermanyPresentIntroducedDAISIE, 2008
GreecePresentNativeUSDA-ARS, 2013
HungaryPresentNative
IcelandPresentIntroducedFlora Islands, 2013
IrelandPresentNativeMilbau and Stout, 2006
ItalyUnconfirmed recordCAB Abstracts; USDA-ARS, 2013
LatviaPresentNativeUSDA-ARS, 2013
LiechtensteinPresentNativeILDIS, 2013
LithuaniaPresentNativeUSDA-ARS, 2013
LuxembourgPresentNativeDAISIE, 2008
MoldovaPresentNativeUSDA-ARS, 2013
NetherlandsPresentIntroducedILDIS, 2013
NorwayPresentIntroducedGederaas L Salvesen I Viken A, 2007
PolandPresentNativeUSDA-ARS, 2013
PortugalPresentPresent based on regional distribution.
-AzoresPresentIntroducedUSDA-ARS, 2013
-MadeiraPresentIntroducedUSDA-ARS, 2013
RomaniaPresentNativeUSDA-ARS, 2013
Russian FederationPresentPresent based on regional distribution.
-Central RussiaPresentNativeUSDA-ARS, 2013
-Northern RussiaPresentNativeUSDA-ARS, 2013
-Southern RussiaPresentNativeUSDA-ARS, 2013
-Western SiberiaPresentNativeUSDA-ARS, 2013
SerbiaPresentNativeNestorovic and Konstantinovic, 2011
SlovakiaPresentIntroducedILDIS, 2013
SpainPresentNativeUSDA-ARS, 2013
SwedenPresentIntroducedDAISIE, 2008
SwitzerlandPresentIntroducedILDIS, 2013
UKUnconfirmed recordDAISIE, 2008
UkrainePresentNativeUSDA-ARS, 2013

Oceania

AustraliaPresentIntroducedUSDA-ARS, 2013
-New South WalesPresentIntroduced Not invasive PlantNet, 2008Weed of cultivation and waste places, rarely common
-QueenslandPresentIntroducedRichardson et al., 2006
-South AustraliaPresentIntroducedRichardson et al., 2006
-TasmaniaPresentIntroducedRichardson et al., 2006
-VictoriaPresent only in captivity/cultivationIntroducedEvans, 2001
-Western AustraliaPresentIntroducedFlorabase, 2013
New ZealandPresentIntroducedWebb et al., 1988

History of Introduction and Spread

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Plants of Melilotus (species unknown) were reported present in North America in 1664 by Boucher (Stevenson, 1969). Its early spread was probably facilitated by beekeepers and agriculturalists, as it can be an important fodder crop and food source for honey bees (Heitlinger, 1975, cited in Turkington et al., 1978).

Risk of Introduction

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The risk of deliberate introduction to further countries is high as M. albus is sometimes seen as a potentially high value fodder crop. Seeds of M. albus are also sometimes introduced as impurities in seeds of other crops such as lucerne (Medicago sativa) (Gucker, 2009).

Habitat

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M. albus is common in sand dune, prairie, bunchgrass and meadow habitats. It is common in desert shrub, sagebrush (Artemisia spp.), pinyon-juniper (Pinus-Juniperinus) and ponderosa pine (P. ponderosa) communities, but in arid areas it may be most common in riparian areas (Gucker, 2009).

M. albus is an early to mid-seral species common on open, disturbed sites. It rarely persists in dense shade and often appears early in the succession of recently disturbed or bare sites (Gucker, 2009).

In Canada, M. albus is found along roadside edges, railway rights-of-way, pastures and disturbed areas (Turkington et al., 1978). Despite its apparent preference for calcareous soils and its unsuitability for acid soils, it is found on a wide range of soil types, including soils with very low nutrient levels, and both fine and coarse-textured soils (Stoa, 1933). It prefers to grow on recently disturbed sites.

In California, Nevada and Florida, USA, M. albus is primarily restricted to recently disturbed sites. Across almost all the USA it is common in riparian areas (Gucker, 2009).

In Alaska, USA, M. albus occupies habitats with extreme weather (Gucker, 2009), with rainfall being below 170 mm in some places and almost 4000 mm in others, with the average annual temperature in inland Alaska as low as -3.3oC (Conn et al., 2008).

In Hawaii, it is 'apparently uncommon in disturbed sites' (Wagner et al., 1999).

M. albus cannot withstand prolonged flooding, but is occasionally found on gravelly open banks beside rivers in Southern Ontario, Canada. It can apparently tolerate moderate salinity, even occurring on soils where salt crystals were visible on the surface (in Alberta, Saskatchewan and Manitoba, Canada; Braidek et al., 1984). It has been promoted in Australia for use on dryland soils affected by salinity (Evans, 2001; Evans and Kearney, 2003). 

Habitat List

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CategoryHabitatPresenceStatus
Terrestrial-managed
Cultivated / agricultural land Present, no further details

Biology and Ecology

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Genetics

The chromosome number is reported to be 2n = 16 (Mulligan, 1957). The presence of a single gene pair distinguishes annual and biennial forms (Clarke, 1935, cited in Turkington et al., 1978).

Reproductive biology

Plants flower in June-July. In Ontario, Canada, M. albus flowers by the last week of June and continues flowering until frosts in the autumn. Flowers remain fresh for about 2 days, and the first seeds ripen by early August (in Ontario). Seeds continue to ripen until late autumn and many remain on the plant over winter (Turkington et al., 1978).

When pistils and stigmas are the same length, self-pollination takes please readily, but when the pistil is longer than the stamens there is little pollination (Clarke, 1935). Barcikowska (1966, cited in Turkington et al., 1978) found that M. albus is cross-fertile but sometimes exhibits high self-fertility in both its annual and biennial forms. Gorz and Haskins (1971) estimated that cross-pollination was 72% in a biennial population and 67% in an annual population. The authors mentioned that inbreeding is widely used in sweetclover (Melilotus) breeding programmes, resulting in a loss of vigour. However, they stress that vigour would be rapidly recovered when inbred lines are used in producing a variety.

Honey bees (Apis mellifera) are the most important pollinators but Coe and Martin (1920, cited in Turkington et al., 1978) listed a wide variety of insects pollinating sweetclover.

Various estimates have been made of the number of seeds produced per plant, ranging from fewer than 100 seeds (for damaged plants, those on infertile ground or suffering from intense competition) to 350,000 seeds (Turkington et al., 1978).

Physiology and phenology

M. albus has a symbiotic relationship with Rhizobium bacteria in its nodules. The highest nitrogen content is in the vegetative parts in late autumn (Dunham, 1933). The compound coumarin, characteristic of Melilotus plants, is concentrated in flower buds and fresh leaves from the tips of the branches (Linton et al., 1963). Roots, stems and mature leaves have very low levels of coumarin.

Day length affects induction of flowering. When grown in a greenhouse at 25.5oC in the day and 20oC at night, biennial plants of M. albus needed at least a 17 hour photoperiod to initiate flowering (Wiggans, 1953, cited in Turkington et al., 1978). However, annual plants flowered during photoperiods of 12-20 hours.

M. albus produces both ‘soft’ seeds, which germinate readily, and a variable proportion of ‘hard seeds’ that are inherently dormant because of the seed coat’s impermeability to water (Gucker, 2009). Although published reports present very variable results, hard seeds appear to be able to survive in the soil for periods estimated at up to 81 years. Germination of hard seeds can be encouraged by heat treatment (including burning), and also by fluctuating temperatures, with the lower temperatures around freezing (Martin, 1945, cited in Gucker, 2009; Van Assche et al., 2003).

Surprisingly, in a species that seems to establish best in open spaces with little surrounding vegetation, Tobe and Gao (2007) claimed that light is not required for germination. There seems to be some evidence that neighbouring vegetation may to some extent act as a nurse crop by moderating seedling establishment conditions (Smith et al., 2004).

Moisture is needed for germination, but, once established, plants are tolerant of extremely dry conditions.

In southern Ontario, Canada, seedlings appear at any time of the year, although there are pronounced peaks of emergence in March-April and September-October (Turkington et al., 1978).

Growth

Smith and Graber (1948, cited in Turkington et al., 1978) described early development of plants of the biennial M. albus. The primary stem becomes branched and a prominent primary root develops. During the first year the crown develops and top growth reaches a maximum in late summer when the roots grow rapidly in size. As root size increases crown buds develop and in the spring of the second year these buds produce rapidly growing stems.

Annual and biennial seedlings are initially similar but by midsummer the top growth of the biennial is more decumbent than that of the annual and buds begin to appear on the crown. Later growth is mainly in the tops in the annual and there is rapid development of the root and crown rhizomes in the biennial (Smith and Gorz, 1965, reported in Turkington et al., 1978).

Longevity

Although the plants of M. albus last only for one or two years, many seeds are the ‘hard’, impermeable type, which can last in the soil for 20 years or more (Stoa, 1933, cited in Turkington et al., 1978; Munn, 1954, cited in Smith and Gorz, 1965).

Population size and structure

Seedlings in fertile loam or clay often arise in clumps, but most die, presumably from competition for light from faster growing neighbours. In gravelly, sandy or stony ground flowering plants are often large and widely spaced, with seldom more than 1 or 2 m-2 (Turkington et al., 1978). Seedling mortality is always high, with less than 25% of emergent seedlings surviving for more than 5 months. Late summer counts at sandy or gravelly locations showed densities of 50-125 plants m-2 of non-flowering plants, the vast majority of which died before the following spring. Widely-spaced plants are often large with many flowering racemes.

At seedling or early vegetative stages M. albus is not a good competitor with vigorous plants of other species, so that plants tend to be restricted to disturbed, ploughed or eroded ground. However, second year plants quickly grow tall in spring and are effective competitors with newly arising weeds (Turkington et al., 1978).

Mowing of roadsides or waste areas usually favours populations (Turkington et al., 1978).

Populations of M. albus can vary in size from year to year, with ‘boom’ populations in some years (Van Riper and Larson, 2009). In South Dakota ‘sweetclover years’ occur when populations are very high (Johnson and Nicholls, 1970, cited in Gucker, 2009).

Nutrition

As with other legume species, M. albus growth is restricted at low levels of sulphur, and application of nitrogen depresses nitrogen fixation and nodulation (Ashford and Bolton, 1961). The species appears to be able to grow on coal ash dumps (Seraya and Komov, 1971, cited in Turkington et al., 1978) and is also salt tolerant to a degree (Evans, 2001). The species has strong deep taproots and can make good growth on soils of moderately low fertility (Smith and Gorz, 1965, cited in Turkington et al., 1978).

Associations

In North America, M. albus grows in a wide range of communities and so is associated with different species (Turkingon et al., 1978). It is associated with herbs and grasses in prairies, with wheat, barley (as a weed in both) or oats (as a companion crop) in crop fields, and with a range of grasses, clover and weedy species in a well-drained abandoned field in Ontario.

In the United States, Gucker (2009) mentions that less common habitats of M. albus include moderately saline marshes, disturbed subalpine fir/grouse whortleberry (Abies lasiocarpa/Vaccinium scoparium) forests in the Northern Rocky Mountains, dry mixed oak and oak-hickory woodlands on the Cumberland Plateau in Tennessee, USA, and hardwood hammocks in Pinellas County, Florida, USA.

In prairies, M. albus commonly occurs on soil mounds formed by wildlife like badgers (Taxidea taxus) and pocket gophers (Higgins and Barker, 1982, cited in Gucker, 2009).

Environmental requirements

M. albus is adapted to a wide range of climatic conditions and is drought tolerant. It only requires adequate moisture for germination and is then capable of development under extremely dry conditions (Turkington et al., 1978). The species is also winter hardy and its range extends as far north as the Yukon and North West Territories in Canada and Alaska in the United States.

M. albus cannot withstand prolonged flooding, but is occasionally found on gravelly open banks beside rivers in Southern Ontario, Canada. Less than 10% of plants survived a 5-day immersion in water at 20oC in Ontario (Turkington et al., 1978). 

Notes on Natural Enemies

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Turkington et al. (1978) listed a number of insects common on M. albus or M. officinalis in London, Ontario, Canada. Frame (2013) named sweetclover weevil (Sitona cylindricollis) as a major pest at establishment that can also damage established stands. Other pests mentioned include the root borer (Walshia miscecoloella), blister beetles (Epicauta spp.) and aphids (Therioaphis riehmi). Frame (2013) also named a number of diseases that affect M. albus: mainly clover rot (Sclerotinia trifoliorum), spring black stem (Ascochyta meliloti), summer black stem (Cercospora davisii), stem canker (Ascochyta caulicola) and root rot (Phytophthora cactorum).

Means of Movement and Dispersal

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Natural dispersal (non-biotic)

The large seeds can be blown a few metres by strong winds, but rain and streams are probably much more important for dispersal (Turkington et al., 1978). The authors found that more than two-thirds of M. albus seeds still floated after 15 minutes in violently agitated water.

Vector transmission (biotic)

M. albus seeds can pass in a germinable state through the digestive system of the moose (Alces alces), at the rate of about 16% of seeds ingested (3,595 of 22,000), most being defecated 2 to 3 days after feeding, but with small numbers sometimes still being defacated 11 days after feeding (Seefeldt et al., 2010). Seeds have also been found to survive passage through white-tailed deer, calves, horses, sheep and pigs (Harmon and Keim, 1934; Myers et al., 2004).

Accidental introduction

Propagules with the outer fruit layers attached can become attached to wet and dry clothing and can be transported in this way (Turkington et al., 1978).

Conn (2010) found seeds of Melilotus (species not determined) in samples of crop, grass and bird seed imported into Alaska, USA. M. albus seeds have been reported as being introduced in imported bird seed (Hanson and Mason, 1985).

Intentional introduction

M. albus was intentionally introduced to North and South America, Australasian and southern Africa, but its escape and naturalisation as an invasive species were probably neither expected nor considered.

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Crop productionGrown as fodder in many places Yes Yes Gucker, 2009

Economic Impact

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M. albus is regarded as a weed of wheat and barley in Canada (Turkington et al., 2013). As a weed of wheat, M. albus can cause melilot or sweet-clover taint of wheat, caused when still-green sweetclover is harvested with wheat, allowing wheat can absorb the odour of sweet clover (Greenshields, 1957).

Royer and Dickinson (1999, cited in Gucker, 2009) noted the association of M. albus with 28 viral plant diseases including beety curly tip, cucumber mosaic and tobacco streak virus. 

Sweet clover disease is a haemorrhagic disease of cattle, occurring mostly in the USA and Canada when mouldy or spoiled sweet clover hay is fed to cattle (Connor, 1997). Large obvious swellings representing subcutaneous haemorrhages are the first clinical signs, usually accompanied by internal haemorrhaging. Sweet clover disease can also occur in sheep, but they are less sensitive. The mycotoxin is dicoumarol, an anti-coagulant, produced from coumaric and melilotic acids in plant tissue by action of the fungi in the hay.

Environmental Impact

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In the USA, many studies have shown that M. albus adversely affects native grass and forb recruitment and growth, as well as restricting the establishment and growth of woody plant species (Gucker, 2009). M. albus is typically more problematic or invasive in northern rather than southern temperate US grasslands, notably in the upper Midwest and Great Plains regions (Gucker, 2009).

Spellman and Wurtz (2011) studied the effects of M. albus on river floodplains in interior Alaska, USA, and found that its invasion had created a novel shade environment in early seral floodplain plant communities. They recommended that the species should be actively managed to prevent its spread into more glacial rivers in Alaska.

M. albus is a particular threat to prairies because it easily invades open areas and may compete for resources with native species, besides fixing nitrogen and thus affecting edaphic conditions. It is also undesirable on prairie reserves because it is a highly visible exotic when in flower.

As a nitrogen fixer, M. albus also has the potential to alter the soil nutrient status and modify the environment in nitrogen-poor ecosystems, often making them more attractive to other invasive species. It has been suggested that the use of Melilotus species for roadside vegetation and rangeland improvement should be discontinued until its effects on ecosystems has been better determined (Lesica and DeLuca, 2000). 

Social Impact

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The tall and vigorous growth of M. albus can hide guide rails and sign posts, creating a hazard for motorists, especially in Northern Ontario, Canada (Turkington et al., 1978).

Risk and Impact Factors

Top of page Invasiveness
  • Proved invasive outside its native range
  • Has a broad native range
  • Abundant in its native range
  • Highly adaptable to different environments
  • Is a habitat generalist
  • Pioneering in disturbed areas
  • Fast growing
  • Has high reproductive potential
  • Has propagules that can remain viable for more than one year
  • Has high genetic variability
Impact outcomes
  • Altered trophic level
  • Negatively impacts animal health
Likelihood of entry/control
  • Highly likely to be transported internationally accidentally
  • Highly likely to be transported internationally deliberately

Uses

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Economic value

M. albus has long been valued for its potential as a fodder crop, for soil and land reclamation, for stabilising soil and roadside cuttings and for honey production. These features led to its adoption in the early 1900s in many parts of the USA. In Illinois, for example, there were 19,000 ha of sweetclover (Melilotus) grown in 1910 and by 1929 this had increased to 310, 000 ha. Similarly, in Nebraska, 12,000 ha were grown in 1920 and 450,000 ha by 1930 (Smith and Gorz, 1965). However, Turkington et al. (1978) pointed out its use in agriculture has been restricted because of the coarseness of its stems, which detracts from its value as a hay crop, and its impermeable seed coat, which means that the seed has to be scarified before it is sown.

Species of Melilotus have been seeded onto burned areas to help in rapid restoration of vegetation cover, but these efforts have not always been successful (Gucker, 2009).

Social benefit

M. albus has several medicinal uses, such as an anticoagulant and as an eye lotion. Its pleasantly-scented dried leaves have been used to scent linens and sleeping quarters (Gucker, 2009).

Environmental services

M. albus can provide food and nectar for native species. For example, Haack (1993) mentioned it as a nectar source for the endangered Karner blue butterfly (Lycaeids melissa samuelis) in Indiana and Wisconsin, USA. Tepedino et al. (2008) suggested that, since M. albus provided nectar and pollen when floral diversity was low and flowers few at Capitol Reef National Park, Utah, USA, many species of native bees may have benefited from the extended flowering season it provides. In parts of Canada, Turkingon et al. (1978) mentioned that pheasants (Phasianus colchicus) nest in sweetclover (Melilotus) stands.

Uses List

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Animal feed, fodder, forage

  • Fodder/animal feed
  • Forage

Environmental

  • Erosion control or dune stabilization
  • Revegetation
  • Soil conservation
  • Soil improvement

Human food and beverage

  • Honey/honey flora

Medicinal, pharmaceutical

  • Traditional/folklore

Similarities to Other Species/Conditions

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M. officinalis (yellow sweetclover) is almost indistinguishable from M. albus except that the latter species has white flowers. M. officinalis is also rather smaller, flowers earlier and is found in drier habitats. The seed pods of M. albus are reticularly veined as opposed to the transversely ridged pods of M. officinalis (Webb et al., 1988).

M. indicus is similar in general appearance to M. officinalis and M. albus but is shorter, its corolla shorter (and yellow, becoming white with age), its inflorescence denser, and its pods similar to those of M. albus, but less distinctly veined (Webb et al., 1988). M. altissima also has yellow flowers, but is a very tall biennial of annual with pubescent ovaries and pods (Turkington et al., 1978).

Prevention and Control

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Prevention

As with many weedy invasive species that can invade native or improved grasslands, the best method of prevention is to maintain healthy natural communities or pastures/grasslands whose vegetation is disturbed as little as possible (Sheley et al., 2009).

Cultural control and sanitary measures

Because M. albus invades disturbed areas, the establishment and maintenance of a uniform, tall and vigorous perennial community can help resist the advance of species like M. albus. DiTomaso and Healy (2003) effectively eliminated M. albus within two years of establishing perennial species cover.

Physical/mechanical control

Gucker (2009) described at length the effects of burning on M. albus. The plant is well adapted to survive fire, especially in its second year. In addition, even if the plants themselves are killed by fire, the seeds can survive for long periods in the soil and their germination is stimulated by heat. Furthermore, the new seedlings take advantage of the lack of competition after fire has passed through an area.

For these reasons, fire can have very mixed effects on M. albus. It can be used to control the species if dormant-season fires used to promote germination of its seed are followed by growing-season fires to kill second-year plants and prevent seed production (Kline, 1986, cited in Gucker, 2009). However, this control method will also reduce native forbs.

Conn and Seefeldt (2009) tested burning M. albus (although their paper described the species as M. officinalis, S. Seefeldt now says it was M. albus; S. Seefeldt, pers. comm., 23 July 2013) with a propane weed burner, combined with cutting plants at 2.5 or 10 cm. Flamed first-year plants wilted immediately after flaming and never recovered, whereas cut first-year plants sent out new branches from meristems at leaf axils below the cut, although still produced fewer seeds than untouched control plants. Second-year plants were damaged but not killed by flaming, and still produced some seeds, as did some of the plants cut at 2.5 cm and most of those cut at 10 cm.

Hand pulling can be used for control, but is usually only effective on very small, isolated populations, and is most effective when the ground is soft enough that the root can be removed (Gucker, 2009).

Cutting or mowing infestations has given mixed results (Gucker, 2009), sometimes reducing population size and seed production but sometimes dispersing the seed even more widely.

Movement control

Seefeldt et al. (2010) observed that moose ingest and spread viable seeds of M. albus and suggested that control of new infestations might be best carried out by following moose trails and monitoring for new patches of the weed.

Biological control

No biocontrol agents have been used for its control, although White et al. (1999) suggested that the American native sweetclover weevil (Sitona cylindricollis) may provide some control when present in large numbers.

Chemical control

Turkington et al. (1978) reported that Melilotus spp. are extremely sensitive to damage from widely used herbicides such as 2,4-D, MCPA, MCPB, 2,4-DB and dicamba, although it becomes harder to kill by its second year.

In Alaska, where M. officinalis is proving invasive, Conn and Seefeldt (2009) tested different herbicides in both glasshouse and field for their effectiveness. In the field they found that chlorsulfuron both reduced plant biomass and prevented seed production. Although clopyralid, 2,4-D and triclopyr reduced biomass, results using these chemicals varied from year to year.

IPM

The abundance of M. albus can be reduced most effectively by integrated management that encourages native or grassland species and limits growth and reproduction of invasive species (Gucker, 2009).

Conn and Seefeldt (2009) suggested that a combination of a range of herbicides (to reduce the chances of development of herbicide resistance or tolerance) and non-chemical methods of control may be most effective in the long term.

Control by utilization

M. albus is eaten by many herbivores, both domestic and feral, including deer, antelope and elk. However, herbivores consuming seed-bearing plants are more likely to spread the species than control it (Gucker, 2009; Seefeldt et al., 2010). M. albus seeds and insect visitors attract waterfowl, game birds and song birds although, again, these may be more important in spreading the seed than controlling the plant (Gucker, 2009).

References

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Contributors

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: Original text by:

Ian Popay, consultant, New Zealand, with the support of Landcare Research.

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