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Key to Ceratophyllum

Ceratophyllaceae

Ceratophyllum

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(c) Thomas - CC-BY
1 Largest leaves forking 1-2× (count branching-nodes from the base of the leaf to the tip of the most-forked division); leaves coarse-textured, stiff, the marginal denticles usually strongly raised on a broad base of green tissue; achene margin wingless, with 2 basal spines or tubercles (these rarely absent), otherwise entire (lacking marginal spines)
(c) Danielson, Erik
1 Largest leaves forking 3-4× (count branching nodes from the base of the leaf to the tip of the most-forked division); leaves fine-textured, flaccid, the marginal denticles not raised on a broad base of green tissue, sometimes obscure or obsolete; achene margin winged, with 2-20 lateral spines 0.1-6.5 mm long (occasionally spineless), with 2 basal spines (these rarely absent).
  2 Achene body (excluding the spines) 3.0-4.5 mm long; first leaves of the plumule simple; [Coastal Plain, NC southward]
(c) Niernberger, Trix - CC0
  2 Achene body (excluding the spines) 4.5-6.0 mm long; first leaves of the plumule forked; [widespread]