Armoracia rusticana

Tall, stout, hairless, stoloniferous plant with a large broad tap root.  Basal leaves large, oblong, toothed and quite erect.  Stem leaves small and short stalked.  Flowers white 8 to 9 mm many in broad panicles.  Fruit rounded, inflated 4 to 6 mm on slender stalks. 

Courtesy of Naturespot - www.naturespot.org.uk