Diplanthera was collected from three tidal zones from various Florida locations. Three growth conditions were found which corresponded to these tidal zones. The first, found in areas exposed at both neap and spring low tides, consisted of dwarf-sized plants. The second, found
in areas exposed only at spring low tides, were intermediate in size between the first and third classifications. The third condition, found in areas never exposed, displayed plants of luxuriant size. Leaf length, leaf width, rhizome thickness, and rhizome internode length were found to be
affected by the environment. The two vegetative characters of leaf apex and internal cellular anatomy were considered by Sauvageau (1890) and later substantiated by Feldmann (1938) as valid for the separation of the two species of Diplanthera, D. uninervis and D. wrightii. The
author found that these factors were variable in D. wrightii, according to the tidal zone in which the plants were found. It is concluded that these two characters are not valid for distinguishing the two species.
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