分株假紫萁（学名：Osmunda cinnamomea），又名假紫萁，为紫萁科紫萁属下的一个种。

Osmundastrum is genus of leptosporangiate ferns in the family Osmundaceae with one accepted species, Osmundastrum cinnamomeum, the cinnamon fern. It is native to the Americas and eastern Asia, growing in swamps, bogs and moist woodlands.

In North America it occurs from southern Labrador west to Ontario, and south through the eastern United States to eastern Mexico and the West Indies; in South America it occurs west to Peru and south to Paraguay. In Asia it occurs from southeastern Siberia south through Japan, Korea, China and ****** to Myanmar, Thailand and Vietnam.