3. Nephrolepis biserrata (Swartz) Schott, Gen. Fil. plate 3. 1834.
Giant sword fern
Aspidium biserratum Swartz, J. Bot. (Schrader) 1800(2): 32. 1801
Stem scales loosely appressed to spreading, concolored or bicolored with pale margins. Tubers absent. Leaves 2--22 × 0.3--3.5 dm. Petiole 0.2--5.4 dm, sparsely to moderately scaly; scales spreading, reddish to light brown throughout (rarely with pale margins). Blade sparsely to densely scaly, glabrous or pubescent, hairs mostly on veins and abaxial, pale to light brown, 0.2--0.7 mm. Rachis 1.8--17 dm, points of pinna attachment 7.5--35 mm apart; scales moderately spaced, pale brown throughout. Central pinnae narrowly deltate to narrowly elliptic-lanceolate, 2.5--23 × 0.5--2 cm, base cuneate, truncate to auriculate-cordate acroscopically, rounded basiscopically, acroscopic lobe small and oblong or absent, margins biserrate to serrulate, apex attenuate; costae adaxially glabrous or densely hairy, hairs erect, pale, 0.3 mm. Indusia circular to horseshoe-shaped, peltate or attached at narrow sinus, 0.8--1.1 mm wide. 2 n = 82.
Terrestrial or less commonly epiphytic in forested, relatively wet habitats, e.g., swamps, but occasionally thickets, roadsides, or clearings; 0 m; Fla.; Mexico; West Indies; Central America; South America; Africa; se Asia.
Some forms of Nephrolepis biserrata closely resemble N . multiflora in pinna shape and indument but lack the distinctively transparent-margined (i.e., bicolored) and persistent petiole scales of the latter species. Nephrolepis multiflora also has more appressed and darker-colored stem scales.