Osmunda regalis
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Osmunda regalis (Old World) Royal Fern |
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| Scientific classification | |
| Kingdom: | Plantae |
| Division: | Pteridophyta |
| Class: | Polypodiopsida / Pteridopsida (disputed) |
| Order: | Osmundales |
| Family: | Osmundaceae |
| Genus: | Osmunda |
| Section: | Euosmunda |
| Species: | O. regalis |
| Binomial name | |
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Osmunda regalis L. |
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Osmunda regalis, or royal fern, is a species of deciduous fern, native to Europe, Africa and Asia, growing in woodland bogs and on the banks of streams. The species is sometimes known as flowering fern due to the appearance of its fertile fronds.
The name Osmunda possibly derives from Osmunder, a Saxon name for the god Thor. The name "royal fern" derives from its being one of the largest and most imposing European ferns. The name has been qualified as "old world royal fern" in some American literature to distinguish it from the closely related American royal fern, O. spectabilis. However this terminology is not found in British literature.
Osmunda regalis produces separate fertile and sterile fronds. The sterile fronds are spreading, 60–160 cm (24–63 in) tall and 30–40 cm (12–16 in) broad, bipinnate, with 7-9 pairs of pinnae up to 30 cm (12 in) long, each pinna with 7-13 pairs of pinnules 2.5-6.5 cm long and 1-2 cm broad. The fertile fronds are erect and shorter, 20-50 cm tall, usually with 2-3 pairs of sterile pinnae at the base, and 7-14 pairs of fertile pinnae above bearing the densely clustered sporangia.
In many areas, O. regalis has become rare as a result of wetland drainage for agriculture.
Osmunda evolved in the southern continent of Gondwana. A permineralized fossil rhizome of fern was discovered in Early Jurassic (Pliensbachian) lahar deposits at Korsaröd in southern Sweden. Authigenic mineral precipitation from hydrothermal brines occurred so rapidly that it preserved cytoplasm, cytosol granules, nuclei, and even chromosomes in various stages of cell division. Morphological studies showed that the plant closely resembles the cinnamon fern, Osmundastrum cinnamomea. The Korsaröd fern fossil and extant Osmundaceae share the same relative genome sizes and ploidy levels. This suggest that neither ploidization events nor notable amounts of gene loss have occurred in the genome of the royal ferns since the Early Jurassic ~180 million years ago.
There are three to four varieties as traditionally construed:
There are three very similar species, Osmunda spectabilis, Osmunda lancea and Osmunda japonica. Recent genetic analysis (Metzgar et al., 2008) has shown that the New World varieties are in a clade that is sister to the Old World varieties of Osmunda regalis. If this is true, then O. lancea and O. japonica should either be regarded as varieties of O. regalis, or, conversely, O. regalis var. spectabilis should be regarded as a separate species, Osmunda spectabilis Willdenow. The var. brasiliensis would then be Osmunda spectabilis Willdenow var. brasiliensis Hooker & Greville.
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