2. Osmunda claytoniana L. (interrupted fern) Pl. 11a; Map 52

Leaves 30–100 cm long, the fertile pinnae produced near the middle of otherwise vegetative leaves. Petioles with orangish brown hairs, becoming glabrate at maturity. Leaf blades 1 time pinnately compound, ovate to oblong in outline. Vegetative pinnae spreading, without a tuft of hairs at the base, deeply lobed, the margins entire. Fertile pinnae ascending, green at maturity, turning dark brown after the spores have been shed. 2n=44. May–July.

Scattered mostly north of the Missouri River, locally south in eastern Missouri to Madison County (eastern U.S. west to Minnesota, Canada, Asia). Rich wooded slopes of ravines, moist ledges of sandstone bluffs, less commonly in bottomland forests and cherty bottoms of sinkholes.

This species is among the most common of the larger ferns to occur in the Glaciated Plains of Missouri.