Rhizomes tuberous, densely branched, clothed with fibres. Fronds coriaceous, tufted, once or twice pinnate. There are six species from various temperate and tropical regions. Named after a Celtic deity.

1. O. regalis. Fern-Royal. - This is the noblest of our native -Ferns, sometimes attaining a height of 10 feet. The fronds are bipinnate, branched, and fertile at the top. It is found in damp, boggy woods in this country, and is widely diffused in the north temperate zone.

O. Claytoniana, syn. O. interrupta, is a dwarf species about 18 inches or 2 feet high, clothed with a ferruginous tomentum when young, with the barren and fertile pinnas intermixed; and O. cinnamdmea has distinct fertile and sterile fronds, the former much the smaller. Both are hardy, and natives of North America, etc.