Kingdom Plantae Order Osmundales Higher classification Polypodiales | Division Pteridophyta Scientific name Osmundaceae Rank Family | |
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Lower classifications Osmunda, Osmunda regalis, Osmunda japonica | ||
The Osmundaceae (Royal Fern Family) is a family of four to six extant genera and ca 25 known 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.
Classification
In the molecular phylogenetic classification of Smith et al. in 2006, the Osmundales, consisting of the single family Osmundaceae, were placed in the leptosporangiate ferns, class Polypodiopsida. The three genera Osmunda, Leptopteris, and Todea were recognized as members of Osmundaceae The publication of a detailed phylogeny of the group by Metzgar et al. in 2008 showed that Osmunda cinnamomea, despite its morphological similarity to Osmunda claytoniana, was sister to the reset of the family, and resurrected the segregate genus Osmundastrum to contain it and render Osmunda monophyletic. This was reflected in the revised classification of Smith et al. in 2008. The linear sequence of Christenhusz et al. (2011), intended for compatibility with the classification of Chase and Reveal (2009) which placed all land plants in Equisetopsida, reclassified Smith's Polypodiopsida as subclass Polypodiidae and placed the Osmundales there. The circumscription of the order and its families was not changed, and its placement remained the same in this arrangement and that of Christenhusz and Chase in 2014. The PPG I classification of 2016 continues to place Osmundales in Polypodiidae, and splits Osmunda further by elevating its subgenera to genera as Claytosmunda and Plenasium.
The following phylogram shows a likely relationship between the Osmundales and the other orders within the Polypodiopsida.
The following phylogram shows a likely relationship between the Osmundaceae genera and subtaxa:
