Indumentum of pubescent hairs with rusty color on young branchlets, leaf rhachis and inflorescences. These are abnormal leaflets on the rhachis of ferns. There is a weak elongated node on the rhachis. The furrow that defines the axis in the pygidium (or rhachis) is almost obsolete. The genus name derives from the Greek words "astreptos" ("inflexible") and "rhachis" ("backbone"). The petiole and the rhachis are sparsely spiked and glandular-fluffy hairy. The rhachis is slightly conical, smooth or slightly ridged.