Mildella fallax

As with most other members of its family, this fern's spore-producing sori develop along the margins of the many-divided leaves' undersurfaces, where the margins are reflexed, providing shelter for the sori. These underturned fern-leaf margins are usually referred to as "false indusia".

In highland central Mexico, Hemionitis fallax differs from a second Mexican species, H. intramarginalis, in that the underturned margins of H fallax are roughly serrate, or saw-toothed, while the underturned margins of H. intramarginalis are only slightly saw-toothed, or serrulate.

Hemionitis fallax is found from Sinaloa and Tamaulipas in northern Mexico to northern Guatemala. Hemionitis fallax occurs in rocky areas and ravines, in forests of oak, oak-pine, fir, tropical deciduous, mesophytic forests in the mountains, and pasturelands.