The Natural History of Ophioglossum palmatum in South Florida

Abstract

Of the sixty or more species in the Ophioglossaceae, only 0. pendulum L. and 0. palmatum L. are epiphytes. Although some authors (Chrysler, 1941; Eames, 1936, fig. 78) have regarded these species as relatively primitive in the genus and have envisioned a reduction series culminating in the more diminutive terrestrial species, others have suggested that they are advanced in most respects (Bower, 1911, 1926; Wagner, 1952). Because detailed information about the gametophytes, spore wall sculpturing, stem structure and development, and venation pattern -among other characters-is not available for most species in the genus, strong adherence to either hypothesis serves little purpose at the present time. Nevertheless, the derivative state of the epiphytic habit in Ophioglossum is supported by its extremely low frequency of occurrence in the genus and the family and the unique frond architectures displayed by both 0. pendulum and 0. palmatum. Numerous discussions of the peculiar features of these epiphytes, as well as speculations about their evolution, have dominated the literature dealing with them, but little has been reported about their natural history and ecology. For this reason, in this paper I would like to relate observations on the natural history of a population of 0. palmatum, the Hand Fern, in southern peninsular Florida. In addition, I shall attempt to place these observations into the context of the natural history of 0. palmatum as it occurs in other parts of its range, as well as that of O. pendulum in the Old World tropics. Ophioglossum pendulum is found throughout the Old World tropics, except for Africa, and is also found in Hawaii (Christensen, 1932; Clausen, 1938, p. 117). It has elongate, ribbon-like blades up to 4 m long and 9 cm wide which often fork in large specimens. Horner (1958), Graf (1970), and Carlquist (1970) each illustrate this species. Each leaf bears one fertile spike which may exceed 50 cm and which is inserted medianly on the sterile portion of the leaf blade. Mature leaf blades are perpendicular to the supporting surface (Wagner, 1952), and stomates are present on both leaf surfaces.