PlantsClubmosses, Spikemosses, and QuillwortsQuillworts — Family Isoetaceae
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Limestone Quillwort —  Isoetes butleri [1]
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Rock Quillwort —  Isoetes lithophila [1]
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Black-footed Quillwort —  Isoetes melanopoda [1,2]
Evidence that species is found in Texas:
  1. USDA Plants Database, advanced search for Texas plants from the United States Department of Agriculture.
  2. Shinners & Mahler's Illustrated Flora of North Central Texas, George M. Diggs, Jr., Barney L. Lipscomb, and Robert J. O'Kennon, Botanical Research Institute of Texas (BRIT), Fort Worth, Texas, 1999. An invaluable resource for identifying Texas plants. Excellent glossary.