Many ferns have specialized fronds that bear sporangia, whereas sterile fronds lack reproductive structures. Although a strong case can be made that the presence of the sporangia will affect the physiology of the frond, only one study could be located that investigated this phenomenon. Thus, ecophysiological (and some morphological) features of fertile fronds were compared with those of sterile fronds of the subtropical epiphytic fern Pyrrosia lingua in Taiwan. Fertile fronds were thicker than sterile fronds, a result of the presence of the large sori. Stomatal sizes and densities did not differ between the two types of fronds. The osmotic potential of liquid expressed from the fertile fronds was more negative than that of the liquid of sterile fronds, although this may be an artifact due to a matric effect of the released spores. No differences in chlorophyll concentrations (area basis only) and a/b ratios were found between sterile and fertile fronds. In situ rates of net CO2 exchange of the fertile fronds were substantially lower than those of the sterile fronds. Similar stomatal conductances and internal CO2 concentrations in the sterile fronds indicated that the efficiency of the photosynthetic apparatus was lower in fertile relative to sterile fronds. The results of this study indicate that the presence of sori on fronds of the epiphytic fern Pyrrosia lingua reduces the photosynthetic capacity of these fronds and, most likely, the productivity of plants harboring many fertile fronds.