An annual of the muddy edges of rivers, lakes, reservoirs, pools, ditches, rutted tracks and roadsides. In the Burren (Co. Clare) it also occurs in limestone solution hollows. It may prefer mildly acidic, nutrient enriched soils. Plants reproduce by seed and also spread by stolons. 0-455 m (Malham Moor, Mid-W. Yorks.).
Though this species is erratic in appearance, there have been many losses, mainly before 1930 but still continuing. Reasons for this include drainage, the infilling of ponds, and lack of grazing. The remarkable increase in Scottish records since the 1962 Atlas may result from better recording or a genuine spread.
Circumpolar Boreo-temperate element.
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Light (Ellenberg): 8
Moisture (Ellenberg): 8
Reaction (Ellenberg): 5
Nitrogen (Ellenberg): 5
Salt Tolerance (Ellenberg): 0
January Mean Temperature (Celsius): 3.5
July Mean Temperature (Celsius): 15.5
Annual Precipitation (mm): 858
Height (cm): 6
Perennation - primary
Life Form - primary
Clonality - primary
Count of 10km squares in Great Britain: 223
Count of 10km squares in Ireland: 13
Count of 10km squares in the Channel Isles: 0
Atlas Change Index: 1
Scarce Atlas Account
Limosella aquatica L.
L. aquatica grows on exposed mud at the edges of rivers, lakes, reservoirs, pools, ditches and winter-flooded ruts in tracks and unmetalled roads. It may be mildly calcifuge - many of its sites were on acidic soils on commons - and is perhaps favoured by nutrient enrichment from animal droppings. It is often found with other annual species, including Eleocharis acicularis, Gnaphalium uliginosum, Juncus bufonius and Rorippa palustris, and with stranded aquatics such as Myriophyllum alterniflorum or species of Ranunculus, It occurs in bare areas on saltmarshes in Hampshire. It is a predominantly lowland species, ascending to 450 metres on Malham Moor.
The species is an ephemeral which germinates very rapidly when mud becomes exposed in the summer and completes its life-cycle before the autumn. Populations vary greatly in size from year to year, and can be very large in those seasons when water levels are low. It has often been recorded at sites after an apparent absence of many years. Dry seeds yielded only 0.8% germination after 27 months (Salisbury 1970) but a greater proportion may remain viable in wet mud. For further details of the reproductive biology of this species, see Salisbury (1967).
L. aquatica is erratic in its appearance, and certainly could not have been found in any one year in all the 10 km squares for which there are pre-1970 records. Nevertheless, like several annuals of exposed mud in small pools, it has undoubtedly suffered a major decline in England and Wales (Salisbury 1970). The reasons for this probably include the surfacing of roads; the drainage of ‘splashy places by the roadside’ (Townsend 1883) and other ephemeral pools; and the fact that many ponds have dried out completely, become overgrown following the cessation of grazing or been engulfed by urban development. Lousley (1976) stresses the former role in Surrey of ducks and geese in creating muddy, nutrient-enriched areas around pools. The sites where the plant has survived tend to be larger waters rather than the small sites which were formerly its most characteristic habitat. It has, however, colonised some newly created habitats such as ‘scrapes’ dug for birds and the margins of gravel pits. In Scotland L. aquatica has been recorded with increasing frequency since 1950 (Leach, Stewart & Ballantyne 1984), probably because this inconspicuous species had been overlooked previously.
It is widespread in northern Europe, with scattered colonies in the mountains further south. It has a circumboreal distribution.
C. D. Preston