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Gametophyte Ecology of the American Hart’s-Tongue Fern: Effects of Temperature and Calcium Availability


Weston L. Testo


This study investigated the gametophyte ecology and physiology of the American hart’s-tongue fern, Phyllitis scolopendrium var. americana. A federally-listed threatened species, the fern is native to eastern North America and found only in lime sinks and glacial plunge ravines with calcium-rich substrates. Greater than ninety percent of the approximately 4000 plants remaining in the United States are found in two counties in central New York, where populations have declined dramatically in recent years. The goal of this work was to generate an improved understanding of potential reasons for the species’ decline through study of its ecology. Gametophytes were grown at 20°C and 25°C and in low-(2.5g/L), medium-(5g/L), and high-(7.5g/L) calcium treatments. Spore germination was of the Vittaria-type, and prothallial plate formation was of the Aspidium-type. Germination rates were similar in all treatments, but growth was significantly slowed in the 25°C, with gametophytes remaining in the protonemal stage of development indefinitely. Calcium affected sexual development, with gametophytes grown in the high-calcium treatments developing gametangia earlier and having higher sporophyte recruitment rates (13.9%) than those grown in medium-(2.3%) or lowcalcium (0.3%) treatments. These findings suggest that P. scolopendrium is particularly susceptible to the effects of climate change and habitat disturbance, and may be outcompeted by other species on account of its slow growth, limited reproductive potential, and extreme habitat specificity.

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