Water Dock - Rumex hydrolapathum

Stout tall much branched plant to 2 metres. Leaves large, rigid broad lanceolate tapered at both ends, lateral veins at right angles to the midrib. Inflorescence dense, flowers in much branched panicles.

other Docks - but it is usually much larger

Large plant at water's edge.  Valves triangular, 3 elongated tubercles

The fruits have a central part, triangular in cross-section, with three membraneous valves surrounding a small, hard 'tubercle'.  The shape and arrangement of valves and tubercles is diagnostic, and close-up photos of fruits and leaves/general habit is needed.

Canal and river banks.

July to September.

Perennial

Fairly frequent in Britain particularly in the southern half.

Fairly frequent in Leicestershire and Rutland. In the 1979 Flora survey of Leicestershire it was found in 64 of the 617 tetrads.

n the current Checklist (Jeeves, 2011) it is listed as Native, occasional

http://www.kenadams.org.uk/esb/Docks.htm