You've certainly seen elk sedge if you've spent any time in our local forests. The large dense vivid green clumps of narrow leaves seem timeless. Even when the heat of summer descends full force, the elk sedge remains more or less the greenest plant on the forest floor. 
 
Small yellow/brown flower spikes appear in the spring, but these are quickly overtaken by an outward cascade of lush narrow leaves. Deer and elk will browse on the sedge in the winter, but this doesn't harm the plant. This species is a fairly slow grower, but can eventually reach around 2 ft in diameter.
 
Plant elk sedge in a shaded area, or one that gets morning sun. Heart-leaf arnica, harebell, and wilcox penstemon are excellent companions.