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
fernorder,
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 Osmundamonophyletic. The phylogeny of Osmunda is shown in the following cladograms.
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.[5]
†O. wehrii Miller (Middle Miocene, Washington state)[7]
Etymology
The derivation of the genus name is uncertain. A common theory is that Osmunda derives from Osmunder, a Saxon name for the god
Thor.[8] Other explanations propose that it is from
Middle English and
Middle French words for a type of fern, or mention an English folk tale of a boatman named Osmund hiding his wife and children in a patch of royal fern during the Danish invasion.[citation needed]
Ecology
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.
^Thomas N. Taylor, Edith L. Taylor, Michael Krings: Paleobotany. The Biology and Evolution of Fossil Plants . Second Edition, Academic Press 2009,
ISBN978-0-12-373972-8 , p. 437-443
^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.
JSTOR2442836.
Pryer, Kathleen M.; Schneider, Harald; Smith, Alan R.; Cranfill, Raymond; Wolf, Paul G.; Hunt, Jeffrey S.; Sipes, Sedonia D. (2001). "Horsetails and ferns are a monophyletic group and the closest living relatives to seed plants". Nature. 409 (6820): 618–622.
Bibcode:
2001Natur.409..618S.
doi:
10.1038/35054555.
PMID11214320.
S2CID4367248.
Smith, Alan R.; Pryer, Kathleen M.; Schuettpelz, Eric; Korall, Petra; Schneider, Harald; Wolf, Paul G. (24 April 2022).
Fern classification(PDF). pp. 417–467., in
Ranker & Haufler (2008)
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