Osmunda

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

Osmunda
Temporal range: Triassic–recent
Osmunda regalis
Scientific classification
Kingdom: Plantae
Clade: Tracheophytes
Class: Polypodiopsida
Order: Osmundales
Family: Osmundaceae
Genus: Osmunda
L.
Type species
Osmunda regalis L.
Species

See text.

Young plant

Description

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".

Taxonomy

Osmunda, the type genus of the fern order, Osmundales has historically been the largest genus in the family Osmundaceae. Smith et al. (2006), who carried out the first higher-level pteridophyte classification published in the molecular phylogenetic era, described three genera in that family, namely Osmunda, Leptopteris, and Todea.[1] The genus has also been treated historically as consisting of a number of subgroups, generally subgenera, Osmunda (3 species), Osmundastrum (2 species), and Plenasium (3–4 species). However, there was suspicion that the genus was not monophyletic.[2]

The publication of a detailed phylogeny of the family by Metzgar et al. in 2008 showed that Osmunda as circumscribed was paraphyletic and that Osmunda cinnamomea, despite its morphological similarity to Osmunda claytoniana, was sister to the rest of the family, and resurrected the segregate genus Osmundastrum, by elevating it from subgenus, to contain it and render Osmunda monophyletic. Their phylogeny of Osmundaceae genera is shown in the following cladogram.[2]

Osmundaceae
 

Osmundastrum (=Osmunda cinnamomea) 1 species

 
 
 
 

Todea 2 species

 
 

Leptopteris 6 species

 
 
Osmunda
 

subgenus Claytosmunda (=Osmunda claytoniana) 1 species

 
 
 

subgenus Plenasium 4 species

 
 

subgenus Osmunda 4 species

 
 
 
 
 

A number of authors have proposed elevating the subgenera to separate genus level,[2] In 2016 the Pteridophyte Phylogeny Group (PPG) classification split Osmunda further by elevating its subgenera to genera as Claytosmunda and Plenasium, leaving only the species originally included in subgenus Osmunda.[3]

One extinct species is placed in the genus:

Hybrids

Previously included

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

Extant species formerly placed in subgenus Claytosmunda are now placed in Claytosmunda in the Pteridophyte Phylogeny Group classification of 2016:[3]:

  • Claytosmunda claytoniana – interrupted fern, Clayton's fern

The following species are placed in Plenasium in the Pteridophyte Phylogeny Group classification of 2016:[3]:

Etymology

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.

Ecology
O. japonica, O. × intermedia, and O. lancea

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 osmundine and used horticulturally, especially in propagating and growing orchids.

References
  1. Smith et al. 2006.
  2. Metzgar et al. 2008.
  3. Pteridophyte Phylogeny Group 2016.
  4. Miller, C.N. jr. (1982). "Osmunda wehrii, a New Species Based on Petrified Rhizomes from the Miocene of Washington". American Journal of Botany. 69 (1): 116–121. doi:10.2307/2442836. JSTOR 2442836.
  5. 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

Bibliography
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