The Carlisle Mosquito Online

Friday, March 30, 2007


(Photo by Kay Fairweather)

Biodiversity Corner
Hypnum imponens - a feather moss

Last Sunday I was walking with friends and our respective dogs in the Towle Woods where there was still a lot of snow. The path was soggy and our progress was slow. There was plenty of time to notice the rocks protruding through the snow — some bald and some wearing mossy green wigs as if they had lost their way to a St. Patrick's Day party. Not many mosses have common names so I sometimes give them a name of my own. One of the mosses on the wig-wearing rocks was Dicranum scoparium whose leaves all lean in the same direction and the books describe it "as if swept with a broom." I think it has a combed-over look and I call it the Donald Trump moss — a topic for another day. For this week I chose instead the more charming fern-like moss that competes in the same habitat with the Donald.

Name. The fern-like moss is Hypnum imponens. Mosses in the genus Hypnum were once known as feather mosses because they were thought to induce sleep and were used to stuff pillows. The genus name comes from the Greek hypnos meaning sleep. The species name, imponens, indicates that this moss can be mistaken for another Hypnum, and so becomes an imposter. I doubt it has felonious intent.

Identifying mosses. Mosses are divided into two groups based on their growth habit. There are the Acrocarps which have an upright habit and grow in tufts like clusters of tiny bottlebrushes. Their spore capsules grow from the tip of the stem. The others, which include the Hypnums, are Pleurocarps. They lie low, quite flat against the substrate, and are much less up-standing than the Acrocarps. The spore capsules can grow from various points along the stem but never from its tip. Both acrocarps and pleurocarps can form dense colonies, but with acrocarps it is quite easy to separate an individual moss plant. Pleurocarps tend to grow in tangled mats from which it is difficult to tease out a single plant.

Distinguishing characteristics. The most obvious characteristic of this moss is that it looks like a miniature fern. It is often slightly orange along the stem. With a hand lens you can see that the leaves grow along the main stem and the side branches. The individual leaves are somewhat cup-shaped and the tip is curved over. It is found on rocks and stumps. It seldom produces spore capsules (which are absolutely necessary for identifying some other mosses).

Safe Harbor. The curved leaf can hold a drop of water and make a good home for tiny water-dwelling animals. The water bears I found to write about in the Biodiversity Corner of December 10, 2004, were living in a patch of Hypnum imponens along with a lot of other little creatures, notably rotifers. Water bears are sometimes called "moss piglets" because of this choice of habitat. Mosses, water bears and rotifers are well suited to one another in that they are all capable of reviving without damage after severe dessication.

References. Illustrated Guide to Some Hornworts, Liverworts and Mosses of Eastern Canada, Robert R. Ireland and Gilda Bellolio-Trucco, 1987; Introduction to New England Bryophytes, Mary Lincoln, 2004; Gathering Moss, Robin Wall Kimmerer.

Please feel free to write the Biodiversity Corner on any living thing large or small that exists in the wild and was seen in Carlisle. If it interests you, it will probably interest others. Send a note to Kay Fairweather at

2007 The Carlisle Mosquito