Osmunda regalis var. spectabilis or royal fern, is one of my favourite ferns. Native to much of eastern North America, I first encountered it near Ottawa a couple summers ago and subsequently in North Carolina, Georgia, and Tennessee. It is not yet in the collections at UBC Botanical Garden, though we hope to procure some wild-collected spores for growing in the Carolinian Forest Garden.
In the past, this was sometimes thought to be equivalent to the Eurasian and African Osmunda regalis. It was also sometimes considered to be its own species, Osmunda spectabilis. Currently (according to USDA GRIN taxonomists), it is recognized as one of three varieties of Osmunda regalis, with the third being the South American Osmunda regalis var. brasiliensis.
Preferring moist habitats such as wet forests or streambanks, royal fern can reach up to 2m (6 ft.) in height under ideal conditions (such as in gardening situations).