Adenophorus periens, a member of the Polypodiaceae family, is a small, pendent, epiphytic (not rooted on the ground) fern usually growing on Metrosideros polymorpha (ohia) trunks. The rhizome (prostrate stem) is covered with small dark, stiff scales 2 to 4 cm (0.8 to 1.6 in) long. Its yellowish green fronds are usually between 10 and 40 cm (4 and 16 in) long and covered with hairs. The fronds have slightly hairy stalks less than 1 cm (0.4 inch) long. Each frond is comprised of oblong or narrowly triangular pinnae (divisions or leaflets) 5 to 15 mm (0.2 to 0.6 in) long with margins that are smooth or toothed and lined with sparse hairs. The pinnae are situated perpendicular to the axis of the midrib, with each pinna twisted such that its upper surface faces upward. Round sori (groups of spore-producing bodies) usually develop in the central portion of the fertile frond, forming two regular rows on each pinna.