Friday, November 9, 2007
Biodiversity Corner: Royal fern
Name. The royal fern is Osmunda regalis, a member of the Osmundaceae family which is named
When and where seen. Royal fern can be found in most of the wet habitats in Carlisle. It likes bogs and swamps and will even grow in water. There are large colonies along the Concord River in the Great Meadows National Wildlife Refuge. The fern in the photo was living happily beside the big pond in the Greenough Land. It is not an evergreen fern, so this time of year you will see it as golden-colored fronds before it dies back for the winter.
Distinguishing characteristics. The royal fern is a lot less ferny than your stereotypical lacy fern. Each frond is "twice-cut" which means that the leaflets on the frond are divided again into sub-leaflets. The more lacy ferns are "thrice-cut." What makes the royal fern so distinctive and less fernlike than even other twice-cut ferns is that there is a lot of space between the sub-leaflets. The fronds look a bit like the compound leaves of a locust tree. Another distinguishing characteristic for ferns in general is the location of the fertile or spore-bearing leaflets. On the royal fern, they occur as the last few leaflets on the tip of a regular frond. They are smaller than the other leaflets. Some ferns, like the cinnamon fern and the sensitive fern, have separate fronds where all the leaflets produce spores. The Osmundas are the tallest native ferns with the royal fern able to reach a height of six feet and thus perhaps giving it a regal bearing. "My name is Osmundas, king of ferns." The royal fern has an underground stem (rhizome) which is thickly coated with roots. The roots not only absorb nutrients from the soil but also act in lieu of bark to protect the stem. The rhizomes with their thick masses of roots are used by humans in the culture of orchids.
Life cycle. Like mosses, ferns require two generations to complete their life cycle, the sporophyte and the gametophyte. The fern we see and know is the sporophyte generation. It has a long life — over 100 years. Each year in early summer it releases ripe spores by the million. Unlike spores from other ferns which remain viable for years, royal fern spores die in just a few days if they don't find a suitable place to germinate. Most that germinate are consumed by herbivores or die from dessication. The few surviving gametophytes are still not out of the woods. The gametes they produce have a very high incidence of genetic defects which means the embryos are unable to develop into the next sporophyte generation. Maybe these genetic mutations that seem such a handicap have allowed the royal fern to survive the ages. Osmunda family ferns were around before the dinosaurs. Fossil records for the family date back 230 million years.
Sources. Peterson Field Guide for Ferns, Boughton Cobb; Royal Fern, Ed Klekowski at www.bio.umass.edu/biology/conn.river/regalis.html.
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© 2007 The Carlisle Mosquito