Medicago lupulina L., Black Medick

Account Summary

Growth form and preferred habitats

This variable little creeping annual, biennial or short-lived perennial legume produces a slender taproot that branches and may penetrate 60 cm deep. Angular stems can be prostrate, decumbent, ascending or erect and vary from 15-80 cm in length and from hairless to densely hairy. Leaves are stipulate, petiolate and trifoliate and the terminal leaflet is stalked. Leaflet shape is variable, even on the same plant. Two cytological forms with differing chromosome numbers have been reported: diploid (2n=16) and tetraploid (2n=32) (Turkington & Cavers 1979).

The remarkably wide distribution of M. lupulina across the globe suggests it has become adapted to a huge range of growing conditions. It typically colonises bare areas in fairly open, dry, lowland, permanent calcareous grassland and it competes and survives best in distinctly infertile conditions. In suitably open conditions, such as wasteland or recently cleared or dug ground or forest margins, it behaves as a ruderal colonist growing extremely rapidly and sometimes even become dominant for a short period. In C England, the established strategy of the species is classified as being intermediate between Ruderal and C-S-R, which recognises it can behave rather differently across the wide range of growing conditions it occupies (Grime et al. 1988, 2007).

M. lupulina is frequently found in moderately disturbed sandy or gravelly soils, where grazing, cutting or trampling curtails the growth of taller, more aggressive species. Black Medick is a typical legume of lowland mown grass on roadside verges, lawns and grass paths, particularly over limestone. The species withstands drought rather well, either surviving vegetatively or as seed, and it avoids strongly acidic or very wet soil conditions (Turkington & Cavers 1979; Grime et al. 1988, 2007). The most acid soil so far reported for this species was pH 4.8 in New Zealand. In moist, somewhat more fertile conditions, individual plants probably have a lifespan of at least four years (Grime et al. 1988, 2007).

M. lupulina can be distinguished from the similar small, yellow pea, Trifolium dubium (Lesser Trefoil), by its bright, as opposed to pale, yellow flowers and by its three apiculate or mucronate leaflets, the terminal one of which is stalked.

Variation

Black Medick is sufficiently variable for five varieties to have been recognised in B & I by Sell & Murrell (2009), all but one of them annual. Of these, var. eriocarpa (Rouy) P.D. Sell occurs in sandy places near the sea and on sandy heaths inland and is considered the most probably native of all five varieties. It also occurs in similar habitats in continental Europe. Var. lupulina probably occurs throughout the range of the species and is a plant of rough grassland on roadsides and waste-ground. It may not be native in B & I. Var. major G. Mey. is a cultivated form previously used for making hay. Today it is mostly found in wild flower seed for planting on waysides. Var. willdenowiana (Boenn.) W.D.J. Koch is also found in cultivated wild flower seed mixtures, although in some habitats it might be native. Var. cupaniana is a perennial variety that originated in S Europe and is a rare introduction in Britain (Sell & Murrell 2009).

Flowering reproduction

M. lupulina regenerates only by seed. The inflorescence is a small, globose or shortly cylindrical flower-head up to 1.5 cm long, containing 20-50 tiny, yellow pea flowers, 2-4 mm long. Well established plants flower continuously right through the summer from April to August. The flowers are usually self-pollinated, but they may also attract bees and other insects that can cross-pollinate them. The black, slightly curved, 3 mm fruit pods each contain a single seed, yet a single robust plant in good growing conditions may produce 2,000 or more seed in a growing season. The pod is indehiscent, the seed and pod being dispersed together as a unit (Turkington & Cavers 1979). In mown lawns and pastures, the plant becomes completely prostrate, most flowers are then borne very close to the soil surface and tend to avoid damage from mowers and larger grazing animals.

Seed dispersal

Dispersal involves birds and other animals ingesting the hard-coated seed along with the plant and internally transporting it. Although they are not adhesive, the small seeds can attach externally to animal coats, human clothing and to mud on machinery. Seeds can also float for up to five days and thus be transported in flowing water (Ridley 1930). As with other grassland legumes, man has also assisted dispersal by transporting seed as impurities in seed mixtures and in fodder crops, so that what originally was a Eurosiberian temperate plant has now become circumpolar.

Germination and phenology

In suitable, bare patch growing conditions in lawns and pastures, seeds can germinate immediately after release from their pod. However, after around ten days, those that mature above the soil surface quickly develop the hard seed dormancy that is so very characteristic of the family. The tough, impermeable seed coat then maintains dormancy through several unfavourable seasons, or for many years of soil burial. The vast majority of individuals overwinter as dormant seeds and germinate in spring, often after a disturbance event like cultivation, animal digging or frost heaving of soil. Under favourable growing conditions, M. lupulina plants will flower within six weeks of seedling emergence and up to three ± distinct generations can arise in a single growing season. In most habitats, the majority of plants die during their first winter, but a small minority may survive up to three years, chiefly in lawns (Turkington & Cavers 1979).

In a comparative study, the presence or absence of moss and the degree of moss in a patchy abandoned grassland habitat in Canada, considerably assisted M. lupulina seedlings to establish, reach flowering capability and survive for more than one season. Moss ground cover reduced evaporation, thereby presumably reducing mortality resulting from drought. It also enabled plants to reproduce repeatedly, whereas without moss, plants simply did not survive long enough to reproduce more than once (Pavone & Reader 1985).

Fermanagh occurrence

M. lupulina is only occasional in Fermanagh, having been found in 29 tetrads (5.5%). It is thinly scattered through the lowlands around Lough Erne, but is slightly more prevalent in the SE of the VC. It typically occurs in grassland habitats, plus in disused quarries and along disused railway waste ground – where presumably thanks to a persistent seed bank and regular disturbance from trampling cattle, it still manages to survive. It also occurs in drier areas of grassland near lakeshores and in urban areas in and around Enniskillen. One odd habitat does occur, however, as it features in a strange admixture of species on a cut-over bog just east of Clonnagore, near the old disused Ulster Canal. The range of species on this peculiar, rather dryer than normal bog site included: Potentilla anserina (Silverweed), Stachys sylvatica (Hedge Woundwort), S. palustris (Marsh Woundwort), Petasites hybridus (Butterbur), Stellaria graminea (Lesser Stitchwort), Ligustrum vulgare (Wild Privet), Barbarea vulgaris (Winter-cress) and Equisetum arvense (Field Horsetail).

British and Irish occurrence

M. lupulina is rather uncommon in both the NW and the far W of Ireland in comparison with the rest of the island. In Britain, it is widespread and common in most of lowland England and Wales, but it becomes more scarce and coastal in Cumbria and Scotland, declining both northwards and westwards (Walters & Perring 1962; Preston et al. 2002).

In both these geographical areas the prevalence of wet, very acid soils is probably the only explanation required for the low presence of this species.

European and world occurrence

This rather variable species is widespread and native in most of Europe, Asia and N Africa. It has been very widely introduced, cultivated and naturalised throughout temperate and subtropical regions of the world including N Europe, Iceland, Greenland, parts of Africa, N & S America, Australia, New Zealand and many other places (Hultén & Fries 1986, Map 1230).

Threats

None.

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