Dennstaedtiales is an order of fern

Fern

A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...

s that includes the world's most abundant fern, Pteridium aquilinum

Pteridium aquilinum

Pteridium aquilinum is a species of fern occurring in temperate and subtropical regions throughout much of the northern hemisphere....

(bracken). Members of the order generally have large, highly divided leaves and have either small, round intramarginal sori with cup-shaped indusia (e.g. Dennstaedtia) or linear marginal sori with a false indusium formed from the reflexed leaf margin (e.g. Pteridium). The morphological diversity among members of the order has confused past taxonomy, but these genera appear to be united in genetic analyses.