A diminutive winter-annual of coastal sand dunes in Wales, on open nutrient-poor substrates which are free-draining but damp in winter; also, in the Channel Islands, on barish gravelly cliff-slopes. It is recorded at other dune sites in England and Scotland, and inland as a casual plant in nurseries and gardens. Lowland.
Several new populations of M. minima have been discovered on dunes since 1980, and it is almost impossible to say whether they are native or alien. A Lancashire population, found in 1996, seems most likely to be the result of spread from the known native sites in Wales.
Suboceanic Southern-temperate element.
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Light (Ellenberg): 9
Moisture (Ellenberg): 3
Reaction (Ellenberg): 7
Nitrogen (Ellenberg): 1
Salt Tolerance (Ellenberg): 0
January Mean Temperature (Celsius): 5.8
July Mean Temperature (Celsius): 16.1
Annual Precipitation (mm): 861
Height (cm): 8
Perennation - primary
Life Form - primary
Clonality - primary
Count of 10km squares in Great Britain: 7
Count of 10km squares in Ireland: 0
Count of 10km squares in the Channel Isles: 10
Atlas Change Index: -0.01
RDB Species Accounts
Mibora minima (L.) Desv. (Poaceae)
Early sand-grass, Eiddil-welltyn Cynnar
Status in Britain: LOWER RISK - Near Threatened.
Status in Europe: Not threatened.
In Britain this species is confined, as a native, to coastal dune systems in Wales. It grows on nutrient-poor sandy soils which are freely draining but damp in winter, and is typically found in small isolated patches of open ground set within a matrix of unsuitable habitat. It occurs in small erosions and rabbit scrapes, stabilising blow-outs or patches of bare sand, and on pathsides. It tolerates a wide range of soil pH levels. Of a wide range of associated herbs and bryophytes, Cerastium diffusum, Erophila verna, Ononis repens, Thymus polytrichus and Tortula ruralis ssp. ruraliformis are the most constant. In the Channel Islands, it is locally frequent, and occurs there on thin, gravelly soils on cliff-slopes.
M. minima is a diminutive annual. Flowering begins in December during mild winters and ends by mid-March, each plant producing a few synchronous, often reddish inflorescences. Despite its small size (often less than 2 cm) it is wind-pollinated and habitually out-breeding: levels of genetic variation are high in British populations, although lower than on mainland Europe (John 1992). Some seeds are shed upon maturity in March to May, others remain attached to the parent plant which dies immediately after seed production. Seed dispersal is often very limited. Germination normally occurs in late summer or autumn, and temporary chilling is necessary to initiate flowering (Pemadasa and Lovell 1974a, 1974b).
M. minima occurs as a native species at several localities on Anglesey and at Whiteford on the Gower peninsula. Its small size and early flowering period make it easily overlooked, and it may occur on other dune systems or even cliff sites. Other dune records are from Studland Heath, from Southport, and from Dirleton, East Lothian, but it is assumed not to be native at any of these sites, and recent investigations have revealed that it was deliberately introduced at Direlton (A.J.Silverside, pers. comm.). As a naturalised weed, probably introduced from the Netherlands, it occurred in plant nurseries in Dorset and Suffolk (perhaps also elsewhere), and grows rarely as a casual.
Since they require areas of suitable open sand which are often temporary, populations on mature dune heath are vulnerable to over-fixation and so depend upon the creation of suitable habitat; small-scale erosion and/or the presence of rabbits are beneficial.
M. minima is largely confined to western Europe and the Iberian peninsula, where it also occurs on old fields and waste ground inland. It is scarce in Belgium and Germany, and most Dutch populations are naturalised introductions, perhaps from southern European stock. Isolated populations also occur around the Mediterranean and in Russia.
R. F. John