bur reed

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of various aquatic or wetland plants of the genus Sparganium, having elongated leaves and ball-like clusters of tiny beaked fruits.

from The Century Dictionary.

• noun The common name of species of Sparganium, so called from their narrow, reed-like leaves and bur-like heads of fruit. The floating bur-reed is S. angustifolium. See Sparganium.

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

• noun marsh plant having elongated linear leaves and round prickly fruit