Scales 2.2-4.4 x 0.6-1 mm, with up to 150 μm long, rather clear cells in the apex; lamina 1-10 x 0.5-3.3 cm, index 1-5; hydathodes pitted.......34 P. petiolosa Scales (2.2-)4-7(-8) x 0.7-1.5 mm, with up to 350 μm long, obscure cells in the apex; lamina 5-22 x 0.8-5.5 cm, index 2-12; hydathodes mostly superficial ........ 26 P. lingua var. lingua

P. petiolosa is usually distinct from P. lingua in its small size, more distinctly pitted hydathodes, more frequently confluent sori, and more thickly coriaceous fronds. The rhizome scales differ from those of P. lingua in the following characters: P. petiolosa — apex of the scales short, ± obtuse, with up to 150 μm long, clear, translucent cells; P. lingua — apex of the scales mostly long, narrow, with up to 350 μm long, narrow, obscure cells. This last character appears to be the most constant one.