A rhizomatous perennial herb of nutrient-rich mud around the cattle-trampled margins of lakes and ponds, in ditches, on canal banks and riversides; also formerly in wet meadows. Lowland.
L. oryzoides has decreased since the 1962 Atlas. Several populations have been lost in the last twenty years, including those in Somerset which were last seen in the early 1990s, and it is now apparently restricted to just three native sites in S.E. England, though it has been re-introduced into two others. The drainage and infilling of ponds and ditches, and possibly the over-zealous maintenance of canal banks, are thought to have contributed to its decline.
European Temperate element; also in C. and E. Asia and N. America.
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Light (Ellenberg): 8
Moisture (Ellenberg): 9
Reaction (Ellenberg): 8
Nitrogen (Ellenberg): 7
Salt Tolerance (Ellenberg): 0
January Mean Temperature (Celsius): 4.2
July Mean Temperature (Celsius): 16.5
Annual Precipitation (mm): 766
Height (cm): 90
Perennation - primary
Life Form - primary
Clonality - primary
Count of 10km squares in Great Britain: 21
Count of 10km squares in Ireland: 0
Count of 10km squares in the Channel Isles: 0
Atlas Change Index: -0.4
Plantatt Conservation Status
RDB Species Accounts
Leersia oryzoides (L.) Sw. (Poaceae)
Status In Britain: ENDANGERED. WCA Schedule 8.
Status in Europe: Near threatened?
L. oryzoides occurs on the margins of drainage ditches, dykes, canals and ponds, and formerly also in marshy fields. It grows on nutrient-rich mud of acid to neutral pH, often close to the water's edge (or occasionally as an emergent), and seems to do best in a rather open community, sometimes in cattle-poached ground. It may occur amongst emergent perennials such as Alisma plantago-aquatica, Glyceria fluitans, G. maxima, Phalaris arundinacea and Sparganium erectum, or lower growing perennials or mud-annuals including Agrostis stolonifera, Bidens cernua, Deschampsia cespitosa, Galium palustre, Lycopus europaeus, Lythrum salicaria, Mentha x verticillata, Persicaria hydropiper and Stachys palustris. Though the habitats in Britain are quite varied, features in common include the presence of nitrogen-rich mud, the proximity of stagnant or slow-flowing water, seasonal inundation, and regular disturbance, which provides areas of bare mud and maintains an open vegetation structure (Birkinshaw 1990b).
This rhizomatous perennial forms loose tufts and patches. It is distinctive when seen at close quarters, and FitzGerald (1988c) notes that "not only the startling cutting power of the finely-spined leaf margins, but the characteristic yellow-green colouring, and the jaunty angle made by the single leaf which tops each stem, become easily recognisable when surveying the plant", but it can be readily passed by if not looked for specially. In Britain it has a long dormant period, and starts to shoot only in late spring. In most years the panicles are not exserted from the sheaths, and are then cleistogamous. Only in years with high temperatures throughout the spring and summer will panicles open fully for cross-pollination, and fruits do not mature until well into September in our climate. Birkinshaw (1990b) has shown that warm summer temperatures may be more important than warm spring temperatures in promoting this development.
Since 1985, L. oryzoides has been recorded at only four sites in Britain. Two are in West Sussex (Shillinglee Lake, where it grows along 120 metres of shore-line, and Amberley Wild Brooks), one in Surrey (the Basingstoke Canal at Sheerwater); one in Somerset, by the Taunton-Bridgwater Canal. The only sizeable population in Britain is at Amberley Wild Brooks, where it occurs in many ditches over an area of 300 hectares. The Sheerwater colony, already very tiny, was destroyed during canal re-construction, but in anticipation of this, plants were successfully transplanted to three other sites by the Basingstoke Canal. In West Sussex, L. oryzoides is no longer known in Arundel Park (where its pond was filled in), and has not been seen since 1982 at Waltham Brooks. In Somerset, it was discovered in 1959 near North Newton in several localities along the Taunton-Bridgwater canal, on both sides of a hectad boundary. It was still present at most, if not all, of these in 1981, but by 1988 only one clump remained. It has not been seen there since 1990 and may now be extinct. Recent searches confirm its extinction in Dorset, and attempts in 1988 and 1990 to re-establish the plant in the New Forest seem to have been unsuccessful.
Drainage of wetland habitats, the cessation of traditional methods of water-course management, and the pollution of waterways have contributed to the decline of L. oryzoides. Regular dredging of water courses provides areas of mud for colonisation, and this has been carried out at Amberley Wild Brooks for many years. The maintenance of high water quality is also essential. At Amberley, monitoring of L. oryzoides over the past fifteen years has shown that the plant grows best on banks of managed, clean-water ditches which are trampled and grazed by cattle.
L. oryzoides has been recorded from southern Finland to Spain and eastwards to temperate Asia and North America. It has markedly decreased throughout the whole of Europe.
M. Briggs and P. A. Harmes