Adiantum amblyopteridium

Adiantum amblyopteridium is a medium-sized fern, growing in clumps with arching fronds. Fronds are closely spaced along the rhizome, which is up to 5 millimeters (0.2 in) in diameter. It bears brown scales, which are lighter at the edges and have somewhat thicker and darker brown cell walls in the center. They are 2 to 3 millimeters (0.08 to 0.1 in) long and 0.3 to 0.5 millimeters (0.01 to 0.02 in) wide, without teeth or projections at the margins. The arching fronds are 60 to 100 centimeters (20 to 40 in) long. The stipe (the stalk of the leaf, below the blade) is dark purple, 30 to 60 centimeters (10 to 20 in) long and 2 to 3 millimeters (0.08 to 0.1 in) in diameter. It makes up from one-half to one-third of the total length of the frond. It bears some comb-shaped scales which are largely worn off as the frond grows. The leaf blades are deltate (triangular) in shape, about 30 to 50 centimeters (10 to 20 in) wide, and bipinnate (cut into pinnae and pinnules). The apex of the blade bears a pinnule similar to those on the remainder of the frond. The rachis (leaf axis) bears tan, lanceolate scales about 1 to 1.5 millimeters (0.039 to 0.059 in) long, with small teeth or cilia projecting from the base. They are not lost over time like those of the stipe. …

It grows on the shaded banks of streams, at altitudes from 50 to 600 meters (160 to 2,000 ft). It is known from Mexico, in the states of Oaxaca, Quintana Roo, and Yucatán, Costa Rica, and Panama.