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Melilotus albus Medik.

Overview
General Information
ID Info
Similar Species
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Family :

Famille :

Fabaceae

Synonym(s) :

Synonyme(s) :

Melilotus officinalis (L.) Lam. subsp. albus (Medik.) H. Ohashi & Tateishi (USDA-ARS 2024)

Melilotus albus Medik. var. annuus H. S. Coe (USDA-ARS 2024)

Melilotus leucanthus W. D. J. Koch ex DC. (USDA-ARS 2024)

Common Name(s) :

Nom(s) commun(s) :

White sweet-clover

(English) (Darbyshire 2003)
Bokhara Clover (English) (GBIF 2019)

Melilotus albus seeds, various views

  • Melilotus albus seeds, various views

  • Melilotus albus seeds, side view

  • Melilotus albus seeds, side view and hilum view

  • Melilotus albus seeds, hilum view

  • Sweet clover, white blossom (Melilotus albus) seeds

  • Sweet clover, white blossom (Melilotus albus) seeds

  • Sweet clover, white blossom (Melilotus albus) seed

  • Sweet clover, white blossom (Melilotus albus) seed

  • Sweet clover, white blossom (Melilotus albus) seed

  • Melilotus spp. Melilotus officinalis and Melilotus albus seed comparison

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Overview

Aperçu

Regulation :

Remarques Réglementation:

    Regulation Notes:

    Distribution :

    Répartition :

    Melilotus albus (white sweet-clover) is native from Europe east to China, North Africa to Myanmar, and Ethiopia to South Africa, growing mostly in the temperate biome (POWO 2024). It is introduced throughout the Americas, northern Europe, northeast Asia, Australia, and New Zealand (POWO 2024).

    In Canada, white sweet-clover is an introduced species which can be found throughout all of the southern provinces as well as the Yukon and Northwest Territories (Brouillet et al. 2010+).

    In the United States, white sweet-clover is an introduced species and is found in every continental state, Alaska, Hawaii, and most outlying islands (USDA-NRCS 2024).

    Habitat and Crop Association :

    Habitat et Cultures Associées :

    White sweet-clover can grow in a wide variety of habitats. It is often found in disturbed areas, roadsides, waste places, ditches, meadows, grasslands, shrub lands, riparian zones, desert shrub, and sand dune areas (FEIS 2009). Sweet-clover under optimal growing conditions has the potential to invade and threaten adjacent native plant communities (Ogle et al. 2008). In China, it has had a serious impact on farmland and grassland. It impedes the growth of native grasslands by shading native species and limiting the availability of sunlight to these species (Chen et al. 2013).

    White sweet-clover occurs as a weed in fields of Triticum aestivum L. (wheat). Often, it is still green when the wheat is harvested. When this occurs, the wheat crop absorbs the smell of the white sweet-clover. This condition is called Sweet Clover Taint (Turkington et al. 1978).

    As an agricultural weed, white sweet-clover is associated with several viral plant diseases, including cucumber mosaic, tobacco streak, and beet curly tip (Royer and Dickinson 1999). For control, removing the plants before they can flower is important to deplete the soil seed bank. Fortunately, it is not listed as having developed herbicide resistance (Heap 2024).

    Economic Use, cultivation area, and Weed Association :

    Utilisation économique, zone de culture et association de mauvaises herbes :

    White sweet-clover is native to the Mediterranean region but has been cultivated and naturalized widely. It is cultivated in Northern and Southern Africa, Temperate Asia including the Arabian Peninsula, Europe, Australasia, regions of Canada and UNITED STATES in North America, and South and Central America (USDA 2022; Abaye 2018).

    White sweet-clover, while potentially a problematic invasive weed, also has value as a forage crop, green manure, rotation crop (Wu et al. 2022), and a nurse crop for revegetation. This is due to its strong taproots that can aerate compacted soil, its ability to fix nitrogen and improve soil nitrogen availability, and its ability to minimize invasion by other less desirable invasive species (FEIS 2009 2009). It is also used in the production of honey (Ogle et al. 2008; Aasen & Bjorge 2009).

    Duration of Life Cycle :

    Durée du cycle vital:

    Annual or biennial

    Dispersal Unit Type :

    Type d’unité de dispersion :

    Legume

    General Information

    RENSEIGNEMENTS GÉNÉRAUX

    Sweet-clover is the most drought tolerant of the commercially available legumes due mainly to the fact that it has a large, deep, widely branched taproot (Ogle et al. 2008; Aasen & Bjorge 2009).

    In the United States, studies have shown that white sweet-clover negatively affects the growth of native grasses, herbs, and woody plant species with strong reductions in seedling survival rates. It is more invasive in northern grasslands than southern grasslands. It is a concern because it readily invades undisturbed open areas where it has the potential to outcompete native species. Because of its ability to fix nitrogen in poor soils and enrich the soil, it has also been known to alter plant community composition (FEIS 2009 2009).

    White sweet-clover produces abundant seeds (up to 350,000 per plant) (Royer and Dickenson 1999) which can be dispersed short distances via wind. Water, animal dispersal where it survives the digestive tract intact, and accidental and purposeful introduction by humans are the most common means by which these seeds are dispersed (CABI 2022).

    Seeds can remain viable in the soil for up to 81 years (Royer and Dickenson 1999).

    Non-native grasslands with white sweet-clover generally support 40% to 60% fewer bird species than native grasslands (FEIS 2009). However, white sweet-clover appears to be an important nectar source for the endangered Karner blue butterfly. In Capitol Reef National Park in Utah, United States, it may be increasing the carrying capacity of native bees there since it blooms at a time when nectar and pollen from native plants are low. Although, it attracts mainly native generalist bees with only one native specialist bee being found utilizing the plant (Tepedino et al. 2008).

    Because of its ability to restore soil, prevent erosion, and enrich nitrogen along with its value as a forage and rotation crop, it has the potential to help make agriculture practices more sustainable and improve food security (Wu et al. 2022). However, its invasiveness should be considered.

    White sweet-clover contains bioactive coumarins known for their pharmacological properties as an anticoagulant, antiviral, and anticancer (Wu et al. 2022). Further research into its medicinal properties is being conducted.

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    Melilotus albus infestation. Photo by John M. Randall, The Nature Conservancy, Bugwood.org

    Identification

    Identification

    <
    >

    • Legume

      Shape

      • Legume shape is oval, which comes to a point at the top and the bottom.
      • The end of the legume opposite the calyx is pointed and curved (Walters 2011).

      Surface Texture

      • Legume is ridged with irregular orientation of ridges.

      Colour

      • Legume is light brown to brownish grey.

      Other Features

      • The calyx often remains attached to the legume.
      • Legumes usually contain only one seed, but occasionally contain two seeds.
      • Seeds produced in a one seeded fruit will be more symmetrical; both sides will be rounded.
      • Seeds which are produced in a two seeded fruit will be flatter on one side, and more rounded on the other side.
    <
    >

    • Seed

      Size

      • Seed length*: 2.0 mm – 2.4 mm; width: 1.2 – 1.6 mm
      *Note: minimum of 10 and maximum of 20 seeds in a normal range of this species using image measurement (ISMA 2020)

      Shape

      • Seed is oval with a slight indentation where the hilum is located

      Surface Texture

      • The seed surface is minutely granular, but these granules can only be clearly observed with a Scanning Electron Microscope (Voronchikhin, 1990). Granules are only faintly visible with a stereo microscope (at 12x magnification), if at all visible. Therefore, given the limitations of a stereo microscope, the surface for the most part, appears smooth but dull.
      • Larger irregular ridges are present on the surface of some seeds.

      Colour

      • When fully mature, most seeds are yellow, and some are slightly greenish yellow (Whitcomb, 1927).
      • As the seeds age, they become brown, reddish brown, or brownish orange.
      • Seeds are usually a solid colour. However, there is limited evidence that some varieties of M. albus can produce seeds with brownish purple mottling as is commonly seen in M. officinalis (Kirk and Stevenson 1931).

      Other Features

      • The hilum is round, and surrounded by rough, papery tissue which is much lighter in colour than the rest of the seed (light, whitish brown). It is bisected with a small slit-like opening (Walters 2011).
      • The lens appears as a small, dark brown raised bump near the hilum at the tip of the cotyledon lobe.
      • Darker pigmentation of the seed coat is usually present from the lens, extending completely around the hilum. In most cases there is also a darker pigmented spot on the seed coat at the tip of the radicle.

      Melilotus albus seeds, various views

    <
    >

    • Embryo

      Shape

      • The embryo is a foliate; bent shape (Martin 1946). The radicle appears to be folded on top of the cotyledons, and they diverge slightly from each other.

    Identification Tips

    CONSEILS POUR L’IDENTIFICATION

    • Seeds are generally oval, with a broad notch in the oval.
    • The radicle is ⅔ to ¾ the length of the cotyledons and diverges slightly from the cotyledons.
    • The space between the cotyledons and the radicle, has the appearance of a small narrow triangle that is lighter in colour than the rest of the seed. The shape and size of this area can be helpful when comparing this species to similar species.
    • Most sweet-clover seeds can stay balanced upright when placed on their narrowest edge (with the hilum facing upwards).
    • Sometimes a wide, shallow radicle furrow is visible on one or more sides of the seed.

     

    Melilotus albus seeds, side view and hilum view

    Additional Botany Information

    AUTRES RENSEIGNEMENTS BOTANIQUES

    Flowers/Inflorescence

    • Flowers appear in unbranched inflorescences 8-20 cm long (racemes), with 40-100 flowers each on individual flower stalks (pedicels) that are 1-2 mm long (WFO 2024). 
    • Leaf-like bracts are 1.5-2 mm (WFO 2024).
    • Calyx made of joined sepals, 2 mm long, with narrowly triangular and somewhat unequal teeth; hairless or appressed-hairy (WFO 2024).
    • Co­rolla is white, 3.5-5 mm (WFO 2024), and looks like a typical pea flower with a standard petal that is larger than the wings and the keel and has a distinctly notched tip; the wings have small hooked earlike appendages (auricles) (WFO 2024). 
    • Ovary is narrowly egg-shaped, each with 2-4 ovules (WFO 2024). 
    • Melilotus albus (white flowers) and Melilotus officinalis (yellow flowers) are difficult to distinguish when not in flower, although the latter tends to be smaller and grows in drier habitats, and has different surface textures on their legumes (Popay 2022).
    • Melilotus indicus (L.) All. is similar in appearance but has a shorter yellow corolla that becomes white as it matures, and its inflorescences are more dense (Popay 2022).
    • Melilotus altissimus Thuill. is also similar but has yellow flowers like Melilotus officinalis and hairy ovaries and legumes (Popay 2022).

    Vegetative Features

    • Erect stems that become hairless with age, 70-200 cm long, rounded in cross-section, and hollow with many branches (WFO 2024).
    • Leaf-like appendages (stipules) are found at the leaf bases and are 6-10 mm long, narrow and taper to a fine point with entire margins (WFO 2024).
    • Leaf stalks (petioles) are slender and shorter than the individual leaflets.
    • Compound leaves arranged alternately on stems with 3 leaflets per leaf (trifoliate).
    • Leaflets are lance-shaped, oblong, linear, or somewhere in between; 15-30 mm long and (4-)6-12 mm wide, with tiny soft hairs (pu¬berulent) on the lower surface, and hairless above, with 12-15 pairs of lateral veins running into the shallowly sharp-toothed (serrated) margins (WFO 2024), although the wedge-shaped leaflet bases are typically entire.

    Melilotus albus inflorescences show numerous short-stalked white pea-like flowers per inflorescence. Photo by Lyrae Willis from Edgewood, BC, Canada.

    Similar Species

    ESPÈCES SEMBLABLES

    Similar species are based on a study of seed morphology of various species, and those with similar dispersal units are identified. The study is limited by physical specimen and literature availability at the time of examination, and possibly impacted by the subjectivity of the authors based on their knowledge and experience. Providing similar species information for seed identification is to make users aware of similarities that could possibly result in misidentification.

    Melilotus officinalis (yellow sweet-clover)

    Yellow sweet-clover seeds look very similar to white sweet-clover seeds. It takes an advanced degree of skill to learn to distinguish the two, but it is possible.

    When observed lying flat on its widest plane:

    • The end opposite the hilum (the bottom of the seed) is slightly wider and more rounded than white sweet-clover.
    • Seeds are thicker, and more rounded on every plane compared to white blossom sweet-clover, except for seeds from a two seeded pod. (In such cases, one side of the seed is flattened.)
    • The curve of the seed at the hilum is shallower. The radicle tip does not protrude as it often does in white sweet-clover.
    • There is very little difference in the thickness of the radicle and the cotyledons. In white blossom sweet-clover there is a noticeable differential between the width of the cotyledons and the radicle.
    • A radicle furrow is often not visible in yellow blossom sweet-clover.
    • The radicle line (interspace between cotyledon and radicle) is wider in yellow blossom, especially at the top of the seed.

    When observed resting on its edge (narrowest plane):

    • Yellow sweet-clover has a longer distance between the hilum and the lens.
    • White sweet-clover sometimes has a shallow radicle furrow. When this furrow is present, it appears as an indentation below the radicle. This feature occasionally presents in yellow sweet-clover, but it occurs more frequently in white sweet-clover.

    Although there has been a history of debate among taxonomists whether these two species should be grouped into one species, there is substantial evidence to support that these two taxa are distinct from one another. Reproductive barriers, DNA sequences, and biochemistry have been used to provide proof that these two species are more closely related to other species than they are genetically similar to each other (Darbyshire and Small 2018).

    Medicago sativa (alfalfa)

    • The main difference between alfalfa and white sweet-clover is the overall shape of the seed. Because alfalfa seeds develop in a multi-seeded pod their shape is irregular and angular.
    • When observed on its narrow plane, it is not rounded outwards like white sweet-clover. Alfalfa often appears twisted.
    • A group of alfalfa seeds are not uniform in shape or size.
    • The radicle line is very narrow compared to that of both white swee- clover, and yellow sweet-clover. It looks like a very narrow triangle that quickly tapers to a thin line.

    Medicago lupulina (black medick)

    • Black medick is oval or slightly kidney shaped with a prominent round bump near the hilum. This bump is the radicle tip.
    • Black medick differs from white sweet-clover in that the cotyledons are very thick. This makes the seed look very round on all planes.
    • The radicle is tightly appressed to the cotyledon; therefore, the radicle line is very narrow.
    • Often the dark blackish brown, or grey pod remains covering the seed after harvest.
    • There is no radicle furrow present.
    • Black medick seeds are noticeably smaller (*length: 2.2 – 1.4 mm; width: 1.5 – 1.1 mm) than white sweet-clover.

    *Note: Minimum and maximum of 12 seeds in a normal range of these species using image measurements.

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    Reference(s)

    Référence(s)

    Aasen, A. and Bjorge, M. 2009 Legumes: Sweet Clover in Kaulbars C. (Ed.) Alberta Forage Manual (2nd Edition): pp. 46-50. Alberta Agriculture and Rural Development. Edmonton, Alberta. Acessed July 11, 2022.

    Abaye, A.O. 2019. Legumes in Common Grasses, Legumes and Forbs of the Eastern United States (Identification and Adaptation). Virginia Polytechnic Institute and State University, Blackburg, VA, pp. 1-46

    Brouillet, L., Coursol, F., Meades, S. J., Favreau, M., Anions, M., Bélisle, P. and Desmet, P. 2010+. VASCAN, the database of vascular plants of Canada. http://data.canadensys.net/vascan/ Accessed March 16, 2024.

    CABI Compendium (CABI) 2022. Melilotus albus (honey clover) https://doi.org/10.1079/cabicompendium.33693 Accessed March 16, 2024.

    Chen, C., Huang, D., Zhang, Y., Zheng, H., & Wang, K. (2013). Invasion of farmland-grassland ecosystems by the exotic sweet clovers, Melilotus officinalis and M. albus. Journal of Food, Agriculture & Environment, 11(1), pp. 1012-1016.

    Darbyshire, S. J. 2003. Inventory of Canadian Agricultural Weeds. Agriculture and Agri-Food Canada, Research Branch. Ottawa, ON.

    Darbyshire, S., Small, E. 2018. Are Melilotus albus and M. officinalis conspecific? , Genetic Resources and Crop Evolution 65 1571 – 1580

    Fire Effects Information System (FEIS) 2009. Melilotus alba, M. officinalis https://www.fs.usda.gov/database/feis/plants/forb/melspp/all.html  Accessed March 20, 2024.

    Global Biodiversity Information Facility (GBIF) Secretariat. 2024. GBIF Backbone Taxonomy. Checklist dataset, https://doi.org/10.15468/39omei via GBIF.org. Accessed March 20, 2024.

    Martin, A.C. 1946. The comparative internal morphology of seeds. American Midland Naturalist 36 513-660.

    Ogle, D., St. John, L., Tilley, D. 2008 Plant Guide for yellow sweetclover (Melilotus officinalis (L.) Lam. and white sweetclover (M. alba Medik.) USDA-Natural Resources Conservation Service, Idaho Plant Materials
    Center, Aberdeen, ID. 83210. Acessed July 11, 2022.

    Plants of the World Online (POWO). 2024. Facilitated by the Royal Botanic Gardens, Kew. Published on the Internet; http://www.plantsoftheworldonline.org/ Accessed March 16, 2024.

    Royer, F. and Dickinson, R. 1999. Weeds of Canada and the Northern United States. The University of Alberta Press, Edmonton, AB.

    The International Herbicide-Resistant Weed Database (IHRWD) 1993-2024 www.weedscience.org Accessed March 16, 2024.

    International Seed Morphology Association (ISMA). 2020. Method for Seed Size Measurement. Version 1.0. ISMA Publication Guide. https://www.idseed.org/authors/details/method_for_seed_size_measurement.html

    Tepedino, V.J., Bradley, B.A., and Griswold, T.L. 2008. Might Flowers of Invasive Plants Increase Native Bee Carrying Capacity? Intimations From Capitol Reef National Park, Utah. Natural Areas Journal 28(1), 44-50.

    Turkington, R., Cavers, P., and Rempel, E., 1978. The biology of Canadian weeds:29. Melilotus alba Desr. and M. officinalis (L.) Lam. Canadian Journal of Plant Science 58 (2): 523-537.

    United States Department of Agriculture-Agricultural Research Services (USDA-ARS). 2024. Germplasm Resources Information Network (GRIN), https://npgsweb.ars-grin.gov/gringlobal/taxon/taxonomysearch Accessed March 16, 2024.

    United States Department of Agriculture-Natural Resources Conservation Service (USDA-NRCS). 2024. The PLANTS Database. National Plant Data Team, Greensboro, NC USA. https://plants.usda.gov/home Accessed March 16, 2024.

    Walters, D.S. 2011. Identification Tool to Weed Disseminules of California Central Valley Table Grape Production Areas. USDA APHIS PPQ CPHST Identification Technology Program, Fort Collins, CO. http://idtools.org/id/table_grape/weed-tool/ Accessed June 28, 2024.

    Wu, F., Duan, Z., Xu, P., Yan, Q., Meng, M., Cao, M., Jones, C. S., Zong, X., Zhou, P., Wang, Y., Luo, K., Wang, S., Yan, Z., Wang, P., Di, H., Ouyang, Z., Wang, Y., and Zhang, J. 2021. Genome and systems biology of Melilotus albus provides insights into coumarins biosynthesis. Plant Biotechnology Journal 20(3), 592-609.

    Author(s)

    AUTEUR(S)

    Lyrae Willis, Environmental Science Freelance Writer

    Janessa Emerson, Canadian Food Inspection Agency, Canada

    Acknowledgement:

    To Krishan Shah, former student of the Canadian Food Inspection Agency, for assistance with the literature search and summary. To Taran Meyer of the Canadian Food Inspection Agency for seed imaging.

    contactus@idseed.org

    Last updated
    on 2023-03-27

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