Wood Dock - Rumex sanguineus

Medium to tall plant more slender than Clustered Dock and with straighter stems and panicles less leafy branches held at a more acute angle to the stem. Fruit with only one valve swollen. The narrow, green leaves become wider and often develop red veins as they mature. The leaf bases of Wood Dock are truncate rather than cordate

A cultivated variety (var. sanguineus) has blood-red leaf veins even when immature, and may occasionally escape from gardens.

other docks

one tubercle well-developed, rounded and smooth 

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.

Woodland rides, path sides, damper shaded places.

June to September.

Perennial.

Common in England & Wales, less common in northern Scotland.

Common in Leicestershire and Rutland. In the 1979 Flora survey of Leicestershire it was found in 491 of the 617 tetrads.

In the current Checklist (Jeeves, 2011) it is listed as Native, Frequent

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