quillwort

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

• noun Any of several vascular, spore-bearing, aquatic or marsh plants of the genus Isoetes, having quill-like leaves.

from The Century Dictionary.

• noun A plant, Isoëtcs lacustris: so called from the quill-like leaves; also, any plant of the genus Isoëles. See lsoëtes and Merlin's-grass.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Bot.) Any plant or species of the genus Isoetes, cryptogamous plants with a cluster of elongated four-tubed rushlike leaves, rising from a corm, and containing spores in their enlarged and excavated bases. There are about seventeen American species, usually growing in the mud under still, shallow water. So called from the shape of the shape of the leaves.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Any of various simple microphyllous vascular plants, of the family Isoetaceae, that resemble rushes and produce spores.

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

• noun any of several spore-bearing aquatic or marsh plants having short rhizomes and leaves resembling quills; worldwide except Polynesia