Osmundaceae

Osmundaceae
Osmunda regalis
Scientific classification
Kingdom:	Plantae
Division:	Pteridophyta
Class:	Polypodiopsida /  Pteridopsida (disputed)
Order:	Osmundales
Family:	Osmundaceae Berchtold & J. Presl
Genera
Osmundastrum Osmunda Todea Leptopteris †Thamnopteris †Zalesskya †Chasmatopteris †Osmundacaulis †Aurealcaulis †Osmundites †Osmundopsis †Todites †Anomopteris †Osmundacidites †Paleosmunda

The Osmundaceae (Royal Fern Family) is a family of four genera and 15-25 species. It is the only fern family of the order Osmundales an order in the class Polypodiopsida (Filicopsida, Pteridopsida, or Leptosporangiate ferns) or in some classifications the only order in the class Osmundopsida. This is an ancient (known from the Upper Permian) and fairly isolated group that is often known as the "flowering ferns" because of the striking aspect of the ripe sporangia in Osmunda and Osmundastrum. In these genera the sporangia are borne naked on non-laminar pinnules, while Todea and Leptopteris bear sporangia naked on laminar pinnules. Ferns in this family are larger than most other ferns.

Ferns of this family form heavy rootstocks with thick mats of wiry roots. Many species form short trunks; in the case of the genus Todea, they are sometimes considered as tree ferns because of the trunk, although it is relatively short.

The leaf tissue ranges from very coarse, almost leathery in the case of the Cinnamon fern (Osmundastrum cinnamomeum), to delicate and translucent, as in the case of the genus Leptopteris.

Recent research on this family has significantly changed our understanding of the relationships of its species. The most striking finding is that O. cinnamomeum, despite its apparent similarity to Osmunda claytoniana, is actually the most anciently-derived species of the family, and so is a sister clade to the clade that comprises Osmunda, Todea, and Leptopteris (Jud et al. 2008), (Metzgar et al. 2008).

The following phylogram shows a likely relationship between the Osmundales and the other orders within the Polypodiopsida.

Polypodiopsida	Osmundales Hymenophyllales Gleicheniales Schizaeales Salviniales Cyatheales Polypodiales

The following phylogram shows a likely relationship between the Osmundaceae genera and subtaxa:

Osmundaceae	Osmundastrum Todea Leptopteris Osmunda Claytosmunda (Osmunda claytoniana group) Plenasium (Osmunda angustifolia group) Euosmunda (Osmunda regalis group)

References

• C.Michael Hogan. 2010. Fern. Encyclopedia of Earth. National council for Science and the Environment. Washington, DC
• Metzgar, Jordan S., Judith E. Skog, Elizabeth A. Zimmer, and Kathleen M. Pryer (2008). "The Paraphyly of Osmunda is Confirmed by Phylogenetic Analyses of Seven Plastid Loci." Systematic Botany, 33(1): pp. 31–36.
• Jud, Nathan, Gar W. Rothwell, and Ruth A. Stockey (2008). "Todea from the Lower Cretaceous of western North America: implications for the phylogeny, systematics, and evolution of modern Osmundaceae." American Journal of Botany, 95:330-339.
• Thomas N. Taylor, Edith L. Taylor, Michael Krings: Paleobotany. The Biology and Evolution of Fossil Plants . Second Edition, Academic Press 2009, ISBN 978-0-12-373972-8, p. 437-443