Osmunda is a genus of primarily temperate-zone ferns of family Osmundaceae. Five to ten species have been listed for this genus.

The species have completely dimorphic fronds or pinnae (hemidimorphic), green photosynthetic sterile fronds, and non-photosynthetic spore-bearing fertile pinnae, with large, naked sporangia. Because of the large mass of sporangia that ripen uniformly at the same time to a showy golden color, the ferns look as if they are in flower, and so this genus is sometimes called the "flowering ferns".

The genus is known in the fossil record back to the Triassic period from fragmentary foliage nearly identical to the living Osmunda claytoniana.

Species

Section Osmunda (Euosmunda)

• Osmunda japonica – Japanese flowering fern
• Osmunda lancea
• Osmunda regalis – Old World royal fern
• Osmunda spectabilis - American royal fern

Section Plenasium

• Osmunda angustifolia
• Osmunda banksiifolia
• Osmunda bromeliifolia
• Osmunda javanica
• Osmunda vachellii

Section Claytosmunda

• Osmunda claytoniana – interrupted fern, Clayton's fern

Hybrids

• Osmunda Xruggii: O. claytoniana X O. spectabilis
• Osmunda mildei: apparently a species, but arising from O. angustifolia X O. japonica

Osmundastrum

The following species actually belong in the separate genus Osmundastrum, even though they have long been regarded as part of Osmunda:

• Osmundastrum asiaticum (syn. Osmunda cinnamomea var. asiatica) – Asian Cinnamon Fern
• Osmundastrum cinnamomeum – Cinnamon Fern

Characteristics

Osmunda species are used as food plants by the larvae of some Lepidoptera species including The Engrailed.

One of the species, the Cinnamon fern (Osmundastrum cinnamomeum) forms huge clonal colonies in swamp areas. These ferns form massive rootstocks with densely-matted, wiry roots. This root mass is an excellent substrate for many epiphytal plants. They are often harvested as osmunda fiber and used horticulturally, especially in propagating and growing orchids.

The derivation of the genus name is uncertain. A leading theory is that it is from an English folk tale of a boatman named Osmund hiding his wife and children in a patch of royal fern during the Danish invasion. Other theories propose that it is from Middle English and Middle French words for a type of fern.

References and external links

• Germplasm Resources Information Network: Osmunda
• Flora of North America: Osmunda
• Species list for Osmunda
• Phipps, C.J., Taylor, T.N., Taylor, E.L., Cuneo, N.R., Boucher, L.D., and Yao, X. (1998). Osmunda (Osmundaceae) from the Triassic of Antarctica: An example of evolutionary stasis. American Journal of Botany 85: 888-895