This monotypic genus is widespread in eastern North America, Central and South America; and a distinct variant occurs in East Asia. Recent molecular research has supported the generic assignment (as reviewed by W). Without its distinctive dimorphic fronds (sterile and fertile), Osmundastrum can be distinguished from Osmunda claytoniana (and regalis) by the tufts of reddish hairs at bases of sterile pinnae. Also, petioles are just slightly shorter than blades (versus ca 1/3 length in claytoniana) and not winged (versus winged); and ultimate segments of pinnae are usually more acute and mucronate (versus rounded).