Rumex aquaticus

Rumex aquaticus L. (Polygonaceae)

Scottish dock, Copag Albannach

Status in Britain: VULNERABLE.

Status in Europe: Not threatened.

R. aquaticus in known in Britain only in southern Loch Lomondside. It occupies a variety of mesotrophic wetland niches within its restricted range: alluvial and gravelly loch shores, river banks, the edges of ditches and streams, marshes and overgrown ox-bow ponds, clearings in wet woods, damp meadowland and even rush-infested abandoned arable ground where the drainage system has broken down. The size of colonies is also very variable, from isolated individuals to impressive assemblages of two hundred or more plants. Amongst the most frequent associates are widespread species such as Carex vesicaria, Deschampsia cespitosa, Equisetum fluviatile, Filipendula ulmaria, Phalaris arundinacea and Sparganium erectum. At three sites R. aquaticus can be found in the more distinguished company of Carex elongata.

This species is perennial, growing up to two metres tall with large basal leaves up to half a metre long. Flowering is in July and August. The valves of the fruit are more or less acute and longer than wide, which immediately distinguishes it from the superficially similar R. longifolius, in which the valves are rounded.

Despite being a conspicuous plant, R. aquaticus was not discovered in Britain until 1935, when R. Mackechnie collected specimens near the mouth of the River Endrick at the south-eastern corner of Loch Lomond (Lousley 1939). Subsequent survey work in the surrounding area by Lousley (1944b), Idle (1968) and others showed R. aquaticus to be well-established between Ross Priory and Balmaha, with a few outlying plants at Arden-Midross and two expanding colonies at Rossdhu on the west wide of the loch. Away from the immediate vicinity of Loch Lomond, an exceptionally strong colony (300 plants in 1995) occurs beside the Endrick above Croftamie, 12 km upstream.

Since 1967, periodic monitoring of R. aquaticus colonies in the lower flood plain of the Endrick has highlighted both gains and losses. On the positive side, colonising plants quickly became established at one locality where wetland restoration successfully reversed a falling water table. The most serious single loss followed the excavation of an unauthorised deep drainage ditch right through the largest known colony of some 250 plants. Far less obvious, but possibly the greatest threat to R. aquaticus in the long term, is introgressive hybridisation with R. obtusifolius. The hybrid (R. x platyphyllos) is all too common wherever R. aquaticus is found, and there are several instances where this fertile hybrid and probable back-crosses with the parent R. obtusifolius have gradually replaced former pure stands of R. aquaticus. Removal of R. obtusifolius from the vicinity of some R. aquaticus colonies has been carried out in an attempt to reduce the incidence of hybridisation (Lusby & Wright 1996). Other associated Rumex species would seem to pose much less of a problem. R. aquaticus x R. crispus (R. x conspersus) has been recorded only about six times and R. aquaticus x R. sanguineus (R. x dumulosus) once or twice in the last sixty years. 

R. aquaticus is widely distributed in central and northern Europe, and in northern Asia, extending well beyond the Arctic Circle.

J. Mitchell