• WordNet 3.6
    • n quillwort any of several spore-bearing aquatic or marsh plants having short rhizomes and leaves resembling quills; worldwide except Polynesia
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Webster's Revised Unabridged Dictionary
    • n Quillwort (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.
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Century Dictionary and Cyclopedia
    • n quillwort A plant, Isoëtcs lacustris: so called from the quill-like leaves; also, any plant of the genus Isoëles. See lsoëtes and Merlin's-grass.
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In literature:

These are comparatively few and large, and are in fours; so they are very like the macrospores of Pillworts or Quillworts.
"The Elements of Botany" by Asa Gray