"The forked fern family (Gleichenaiceae) is very common throughout the mesozoic. These grow in dense thickets in open environments and on slopes. Low browsing herbivores are fond of these as well, their soft fronds in particular are sought after by ankylosaurs."
Gleichenaiceae (correctly spelled Gleicheniaceae) is the family that consists of ferns known as forked ferns. Due to being softer than the hard ferns and chain ferns, they are probably a more ideal food source for the various herbivores in Hell Creek.