An annual found in open sandy and gravelly habitats by the coast. It occurs in short, open grassland on summer-parched banks and cliffs with other annuals, particularly in S.W. England. Inland, like other Medicago species, it occurs as a casual, especially with wool shoddy. Lowland.
M. polymorpha has declined at its coastal stations through scrub encroachment and lack of grazing, although it may be overlooked or confused with M. arabica. It is much scarcer nowadays as a casual inland.
Light (Ellenberg): 9
Moisture (Ellenberg): 4
Reaction (Ellenberg): 5
Nitrogen (Ellenberg): 5
Salt Tolerance (Ellenberg): 0
January Mean Temperature (Celsius): 5
July Mean Temperature (Celsius): 16.4
Annual Precipitation (mm): 801
Height (cm): 60
Perennation - primary
Life Form - primary
Clonality - primary
Count of 10km squares in Great Britain: 118
Count of 10km squares in Ireland: 0
Count of 10km squares in the Channel Isles: 12
Atlas Change Index: -1.34
Scarce Atlas Account
Medicago polymorpha L.
This species is found in a variety of open, sandy or gravelly habitats near the sea. In south-west England, for example, it occurs in short summer-parched coastal grasslands with such species as Arenaria serpyllifolia, Crepis capillaris, Medicago arabica, Torilis nodosa, Trifolium campestre and T. dubium. It also grows in areas kept open by trampling. It occurs as an alien on road verges and rubbish tips, where it is usually casual but sometimes persists. It has often been introduced with wool shoddy.
It is an annual, reproducing entirely by seed, which germinates mainly in the autumn. It probably requires bare ground for germination and seedling establishment.
It appears to be much less frequent now than previously in its native habitats. Removal of grazing may have been responsible for its demise at some sites, and there are several populations in south-west England currently at risk from scrub encroachment following agricultural abandonment. Some sites may have been lost through habitat destruction, for example by sea-defence work and building developments. However, this species is probably under-recorded, as it can easily be overlooked, especially when accompanied by M. arabica.
M. polymorpha is widespread in Europe, extending northwards as a native to Britain but found as an occasional casual further north. It is also found in North Africa and throughout western Asia; Small & Jomphe (1989) describe it as "adventive where not limited by cold, drought, and waterlogging of soil".
The closely related M. arabica, which has a more northerly world distribution, has been a much more successful colonist of inland habitats.
S. J. Leach & D. A. Pearman