Claytosmunda is a genus of fern. It has only one species, Claytosmunda claytoniana, the interrupted fern, native to Eastern Asia and eastern North America, in the Eastern United States and Eastern Canada. The specific epithet is named after the English-born Virginian botanist John Clayton. "Interrupted" describes the gap in middle of the blade left by the fertile portions after they wither and eventually fall off. The plant is known from fossils to have grown in Europe, showing a previous circumboreal distribution. Fragmentary foliage resembling Claytosmunda claytoniana has been found in the fossil record as far back as the Triassic, and is known as †Osmunda claytoniites. C. claytoniana is a paramount example of evolutionary stasis. Paleontological evidence indicates it has remained unchanged, even at the level of fossilized nuclei and chromosomes, for at least 180 million years.
Description
Claytosmunda claytoniana fronds are bipinnate, tall and broad, the blade formed of alternate segments forming an arching blade tightening to a pointed end. The lower end is also slightly thinner than the rest of the frond because the first segments are shorter. Three to seven short, cinnamon-colored fertile segments are inserted in the middle of the length, giving the plant its name. In their absence, the plant in all its stages appears similar to Osmundastrum cinnamomeum. The base of the segments distinguishes the two species: where O. cinnamomeum has typical felt-like hairs, the few hairs present on C. claytoniana are extremely short, usually requiring a magnifying glass to see well. Like other species in the family Osmundaceae, it grows a very large rhizome, with persistent stipe bases from previous years. It forms small, dense colonies, spreading locally through its rhizome, and often forming fairy rings.
Taxonomy
The species was first described by Carl Linnaeus in 1753, as Osmunda claytoniana. In 2005, it was recognized as being somewhat different from other species in the genus by being placed in a separate subgenus, Osmunda subgenus Claytosmunda. In 2016, the subgenus was raised to a new genus, Claytosmunda, as part of the Pteridophyte Phylogeny Group classification. The change of genus is recognized in some taxonomic databases. Others place the species in the genus Osmundastrum.
Claytosmunda claytoniana is found in humid zones, mostly in forests, but also in more open habitats and biomes, although rarely in bogs. The interrupted fern is often found alongside ostrich, cinnamon and sensitive ferns.
Hybrids
, is a hybrid between C. claytoniana and O. spectabilis. The hybrid is considered important because it suggests a closer genetic relationship between C. claytoniana and O. spectabilis than between C. claytoniana and O. cinnamomeum. Osmunda × ruggii is sterile and is known from only about two natural populations, despite the many areas in which both C. claytoniana and O. spectabilis are found.
Unlike those of the ostrich fern, the interrupted fern's fiddleheads are not readily edible, due to their bitter taste and a tendency to cause diarrhea. The base of the stipe and very young buds are edible. Overuse may kill the crown.
