Synonym: [Hillebrand's Pollpodium hookeri Brack. ß var.]

Endemic

Name honors Charles Noyes Forbes (1883-1920), botanist with the Bishop Museum, who collected in Hawai 'i from 1908 to 1920.

Plants small, epiphytic. Rhizomes decum-bent to erect, 3-5 mm diam. Fronds arranged in tufts at rhizome tips, spreading, 10-17 x 0.5-1 cm. Stipes 0.5-2 cm long, mostly 1/15-1/3 frond length, dark brown, scales small, tightly clustered, overlapping, pale tan, stipes also with frequent to common hairs as on blade. Blades broadly linear, widest at mid-blade with tapering tips and bases, gradually narrowing to stipes, margins entire, hairs on blades frequent to common, 0.5-2 mm long, stiff, black. Sori medial, round to oval, arranged in regular single rows on either side of midrib, paraphyses consisting of sharp-tipped hairs.

Recently recognized, occasional to frequent epiphyte in wet forests, 500-1,200 m, Kaua'i, Moloka 'i, and Maui. Grammitis forbesiana may be a fertile hybrid between G. baldwinii and G. hookeri, or a species with intermediate characters. Further study of this recently recognized fern, including chromosome counts, isozymes, DNA, and scanning electron microscopy of the spores, is needed.

Grammitis forbesiana, found in high-elevation wet forests on Kaua'i, Moloka'i, and Maui, is intermediate between G. baldwinii and G. hookeri in sorus location, hair abundance, frond shape, and stipe length.