Carex atrata Black Alpine-sedge
I usually see this plant on or near the ledges in the Ben lawers corries in Scotland and at its tallest it would be under 20 cm tall. Stace says it can be up to 55 cm but I've never seen it grow anywhere near that height.
Until, that is, I saw these monsters in Switzerland. They were probably about 70 or 80 cm tall and so I didn't recognize them at all. I do expect differences in habit and habitat in plants seen in the British Isles and those seen abroad but this was truly amazing.
C. atrata, also known as Jet Sedge, is a circumpolar sub arctic species found as far north as Greenland, and as far south as Turkistan and the Rockies in north America.
Near station on walk to Alp Grüm, Engadine, Switzerland 9th July 2010
Added on August 3rd 2010, updated 12th Nov 2014