Blechnum cordatum is a tolerant, not vulnerable species, with large sporophytes, erect, scaly rhizomes, dimorphic fronds with scaly stipes and axes; lanceolate sterile laminae with lanceolate to oblong, coriaceae, finely denticulate to serrate, superficially scaly and hairy, attached by costa (peciolulate) pinnae, with cuneate- truncate to subcordate or auriculate bases, and narrowly lanceolate fertile laminae with vegetative tissue of pinnae reduced to the portion which support the undulate to erose indusia and continuous coenosorus. Veins are free, simple, geminate and furcate, the last ramdomly dividing at different distances from the costa, all ending in large, active hydathodes. Aerophores, located only at the base of pinnae, may be absent. Spores have a cristate-reticulate perispore with filiform, ramified processes, and a smooth to granulate exospore.

The species grows in Middle America, Antillas and South America, from Venezuela and Colombia to Bolivia, SE and centre of Brazil, Paraguay, Argentina, centre and S of Chile, Juan Fernández and Marianas Islands.