eriophorum

from The Century Dictionary.

• noun A small genus of cyperaceous plants, found in the cooler parts of the northern hemisphere, distinguished by the delicate capillary bristles of the perianth, which lengthen greatly after flowering, and form a conspicuous cotton-like tuft; the cotton-grass.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun cotton grass