Trefoils, Medicks & Allies
What are they?
This group of yellow-flowered plants consists of species that are mostly short annuals or low-growing perennials. The name 'trefoil' comes from the French, meaning 'three leaves' and the word has been used rather loosely for several plant groups in the pea family, most notably members of the genera Trifolium and Lotus, but also a few others. Thus, not all 'trefoils' are necessarily closely-related, but they are all in the pea family.
Where are they found?
Trefoils are mostly plants of short-grass habitats and largely can be found on heathland, mown lawns, roadsides and similar grassy banks. Medicks are mostly found in open, disturbed habitats, such as arable margins, flower borders, gravel paths and similar places. Many of the trefoils, but especially Common Bird's-foot Trefoil and Lesser Trefoil, are widely sown as components of grass seed mixes for their nitrogen-fixing abilities, which enriches the soil and aids the young grass.
Identification
Leaf structure and overall flower features will get you into the right area to start with. When it comes to the medicks, important features include the leaf stipules (leafy extensions at the base of the leaf stalk) and details of the fruits. For the Lotus species, you will need to check leaf detail and the appearance of the calyx teeth at the base of the flower. The Trifolium species are best told apart by details of the leaves and of the fruiting heads.
Common Bird's-foot-trefoil Lotus corniculatus
A common native in sandy and chalky grassland habitats but also widely introduced as a component of grass seed mixes, often involving different subspecies to our native plant. Flowers June to September. A low-growing plant to 40cm - less when growing in cropped turf. Flowers may be clear yellow or tinged with red and the calyx teeth are erect in bud. The leaves are rather variable in the width of the three leaflets, but generally have broad stipules at the base that give the impression of their being five leaflets. Different subspecies from continental Europe are now commonplace in the countryside and often originate from so-called 'wildflower mixes'. These plants tend to be taller (to 60cm) than our native plants and often have narrower leaflets and hollow stems. Such plants hybridise with native plants and produce a range of intermediates and care should be taken to tell them apart from Greater Bird's-foot Trefoil.
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Greater Bird's-foot-trefoil Lotus pedunculatus
A common native of damp grassland, marshes and fens. Flowers June to September. A tall-growing plant to 80cm, tallest in tall-herb fen communities. Flowers usually clear yellow but occasionally tinged with red; the calyx teeth are spreading in bud. The leaves have broad leaflets and stipules and usually have a scattering of longish, white hairs. The stems are hollow (usually solid in Common Bird's-foot Trefoil but see that species description above).
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Narrow-leaved Bird's-foot-trefoil Lotus tenuis
Native. Fairly common on grassy river walls and banks close to the coast in Suffolk and in the lower Norfolk Broads but strangely absent from similar habitat on the Norfolk coast and around the Wash. Occasionally found inland on disturbed ground where introduced. Flowers June to August. A low-growing, patch-forming species. Flowers usually clear yellow, the upper two calyx teeth usually converging on each other. The leaves have three, very narrow leaflets and two, narrow, leaflet-like stipules.
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Hairy Bird's-foot-trefoil Lotus subbiflorus
A rare native in the UK, mostly confined to coastal sites in the South-west. A rare introduction in East Anglia, having been recorded once each in Blakeney and Southwold. Resembles other bird's-foot trefoils but is distinctly covered in long, silky white hairs.
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Lesser Trefoil Trifolium dubium
Native. Very common throughout the region in all kinds of grassy places. Often introduced as a component of grass seed mixes. Flowers April to October. A low-growing annual, 10-25cm in height. Flowers are small, in tight heads, the standard petal lying flat and not standing upright. Leaflets are broad and clover-like. The seedheads develop as pendant clusters and do not inflate as they mature.
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Hop Trefoil Trifolium campestre
Native. Widespread in many kinds of grassy places on drier soils; much less common in the Broads area and the Fens. Flowers April to October. A low-growing annual to 30cm in height. Flowers are small, in tight heads, the standard petal much enlarged like an upturned boat and soon inflating as the flowers mature. Leaves are clover-like with the middle of the three leaflets having a stalked base. The seedheads become straw-coloured as they ripen and somewhat resemble small hops.
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Large Trefoil Trifolium aureum
Introduced from mainland Europe. Rare, with old records from Suffolk and Cambridgeshire. A casual that has not become established. Flowers June to August. A low-growing annual to 30cm in height. Flowers are small, in tight heads, the standard petal much enlarged like an upturned boat and soon inflating as the flowers mature. Flowerheads average a little larger than those of Hop Trefoil. Leaves are clover-like with the middle of the three leaflets not having a stalked base. The seedheads become straw-coloured as they ripen and somewhat resemble small hops.
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Slender Trefoil Trifolium micranthum
Native. Uncommon, though widespread in dry grassland and becoming further established as a weed in garden lawns. Flowers June to August. A low-growing annual to 10cm in height. Flowers are small and narrow, in open clusters of six or less (typically more than 10 in Lesser Trefoil, but beware of small individuals of that species). Leaves are trifoliate and clover-like. The seedheads develop as pendant clusters and do not inflate as they mature.
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Black Medick Medicago lupulina
Native. Widespread and very common in most types of grassland and as an urban weed and a plant of rough and disturbed ground. Flowers May to September. A low-growing annual or short-lived perennial which may be mat-forming on open ground or may grow to 50cm in height among taller vegetation. Pale yellow flowers are small and carried in dense clusters that form a rounded oval shape (compare with the more spiky head of Lesser Trefoil). Leaves are trifoliate and clover-like, each leaflet having a distinct point at the tip (a mucronate tip). The seedheads develop as a dense cluster of green, then black, circular seeds.
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Spotted Medick Medicago arabica
Native. Widespread and common in grassy and disturbed places. Most common towards coastal areas but seemingly becoming more common further inland over the past 20 years or so. Flowers May to September. A low-growing annual which may be hairy or smooth. Bright yellow flowers are carried singly or in open clusters of up to five. Leaves are trifoliate and clover-like, each leaflet having a black spot on it, though these spots vary in intensity and may often be poorly defines. Leaf stipules are shallowly toothed. The seedheads develop as a small cluster of spiny fruits.
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Toothed Medick Medicago polymorpha
A rare native at a handful of sandy locations around our coastline. Elsewhere an uncommon and non-established introduction from the continent. Flowers May to September. A prostrate, hairless annual. Small, bright yellow flowers are carried singly or in open clusters of up to eight. Leaves are trifoliate and very like those of Spotted Medick, but without the spots. Leaf stipules are deeply toothed. The seedheads develop as a small cluster of rounded, spiny fruits.
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Bur Medick Medicago minima
A rare native with a stronghold on sandy soil in Breckland and in a few scattered places in the Suffolk Sandlings. Flowers June to August. A small, prostrate, hairy annual plant that may require getting down on hands and knees to find! Tiny flowers (2.5-4mm long) are carried singly or in clusters of up to five. Leaf stipules are almost entire, not obviously toothed. The seedheads develop as a cluster of tightly rounded, slightly hairy, spiny fruits.
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Sickle Medick Medicago sativa ssp. falcata
A native plant with a stronghold on sandy soil in Breckland and in a few scattered places elsewhere, especially near the coast. Flowers June to August. A rather sprawly perennial plant, growing to around 60cm or so in height and more bushy than other medicks. Yellow flowers are carried in tight clusters. The seedheads become curved and sickle-shaped as they develop. This plant is closely related to Lucerne and often grows with it. The two hybridise to produce plants with an array of often bizarrely-coloured flowers (see Lucernes).
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