Regalis means regal, or of outstanding merit.
Rhizome: erect, massive, forming a trunk, occasionally branching, hairs and old stipe bases woven together with black, fibrous roots.
Frond: 120 cm high by 25 cm wide, though sometimes much taller, deciduous, dimorphic, blade/stipe ratio: 1:1.
Stipe: stipules (flared leaf base), unique to the family/genus, hairy when young, soon glabrous, vascular bundles: 1 in a U-shape where the top of the arms continue to curl.
Blade: 2-pinnate, rachis grooved, somewhat waxy, shedding water, reddish to light brown hairs, soon falling.
Pinnae: 5 to 9 pair, catadromous, often jointed at the rachis, rotated to the horizontal; on fertile fronds usually the two to four lowest pair are sterile; pinnules oblong, to 8 cm, 8-12 pairs plus a terminal pinnule; margins almost entire, the tip of the pinnules serrate; veins free, forked.
Sori: none, indusium: absent, sporangia: large, globose, tan or black when mature, spores green, maturity: early to midsummer.
Dimensionality: horizontal pinnae.
Habitat: wet, acidic swamps, bogs.
Distribution: Europe and northern Africa, eastern North America.
Hardy to -40°C, USDA Zone 2.
Distinguished from other Osmunda by having fertile pinnae above sterile pinnae and 2-pinnate; distinguish from all other ferns by the generic characters: no sorus, no indusium, naked sporangium, winged stipe bases.