Adiantum amblyopteridium is a maidenhair fern of Mexico and Central America. It has twice-divided, arching fronds with dark purple stalks, and grows on shaded banks and lakeshores. It was first described as a distinct species in 1988, based on material from Oaxaca.
Description Adiantum amblyopteridium is a medium-sized fern, growing in clumps with arching fronds. Fronds are closely spaced along the rhizome, which is up to 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 long and wide, without teeth or projections at the margins.
The arching fronds are long. The stipe (the stalk of the leaf, below the blade) is dark purple, long and 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 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 long, with small teeth or cilia projecting from the base. They are not lost over time like those of the stipe. Each frond has 6 to 9 pairs of pinnae, long and broad, and divided into pinnules. The lower pinnules are triangular to fan-shaped, while the pinna apex is merely lobed (rather than divided into pinnules) and elongate. The largest pinnules are by , with a blunt and broadly rounded apex. There is no joint at the base of the pinnule where it meets the stalk. The veins are free (not netted) and fork, terminating in tiny teeth at the margin of the leaf blade. Scattered tan, comb-shaped scales about 0.8 mm long are present on the underside of the leaf only. Idioblasts (silica bodies) are visible on both sides of the leaf.
On fertile pinnules, 6 to 10 sori are present. The false indusia formed from the leaf margin are long, oblong to crescent-shaped, and lack hairs or scales. The glabrous (false) indusia, presence of multiple sori per pinnule, and broadly rounded tips distinguish A. amblyopteridium from other bipinnate Mexican species with idioblasts, A. pulverulentum and A. trichochlaenum.
Taxonomy The species was first described by John T. Mickel and Joe Beitel in 1988, based on material collected by Mickel in Pochutla District, Oaxaca. The type specimen is Mickel 5140, at the New York Botanical Garden herbarium.
A. ambylopteridium and A. obliquum are believed to be the two ancestors of the allopolyploid A. oaxacanum.
Distribution and habitat It grows on the shaded banks of streams, at altitudes from . It is known from Mexico, in the states of Oaxaca, Quintana Roo, and Yucatán, Costa Rica, and Panama.
Notes and references References
Works cited