Friday, March 25, 2005
Soft Hair Cap Moss
Moss life cycle: Mosses have a life cycle that involves an alternation of generations that is different from seed-bearing flowering plants. The dominant generation of a moss is the gametophyte (the haploid form). This is the little leafy photosynthetic plant that we see growing in soft mounds on banks, at the base of trees, in the cracks in paths, and in all sorts of shady, moist locations. The gametophyte has male and female parts, often on separate plants. They are dependent on moisture for fertilization since the sperm must swim to the egg. The fertilized egg does not give rise to a new moss plant but to the intervening generation, the sporophyte (the diploid form) which can be small and often inconspicuous. It does not photosynthesize; it grows directly on the gametophyte, from which it draws nutrition. The sporophyte is made up of a capsule on the end of a stalk called a seta. The sporophyte creates and disperses spores which germinate and grow into new moss plants.
Identifying mosses: There are two big divisions in mosses that are the starting points for identification. Acrocarps have an upright habit and grow in tufts a bit like tiny bottlebrushes. The seta emerges from the tip of the stem in the center of the tuft. Pleurocarps are more flat to the substrate; they grow in mats and the setae arise at various points along the stem. Both acrocarps and pleurocarps can form densely populated colonies, but with acrocarps it is quite easy to separate an individual plant, unlike one from the tangled mats of pleurocarps. For each type of growth form, close examination of the leaves and the spore capsules with a hand lens is generally necessary for identification. Some mosses cannot be identified without the sporophyte generation.
Name: The soft hair cap moss is Polytrichum piliferum. Polytrichum means many hairs and refers to the hairy cap, or calyptra, on the spore capsule. There are several species of Polytrichum — all are known as hair cap mosses. The species name, piliferum, means "hair bearing". Hair is obviously important to the hair-bearing hairy cap moss — I think of it as the Johnny Damon moss. (There is another moss with very long slender leaves that are usually swept in the same direction — it has a certain look that makes me call it the Donald Trump moss.) The soft hair cap moss is also known as the awned hair cap moss. (An awn is a bristle-like extension of the leaf midrib.)
When and where found: There is a large colony of this moss on the soil bank at the entrance to the Foss Farm parking lot. On March 18, when there was still a lot of snow on surrounding flatter ground, the moss on this bare patch of ground was sporting fresh young sporophytes. This moss is sharing the bank with a more conspicuous brighter green moss of much finer texture; and right in their midst, keeping the peace, is a troop of British Soldiers.
Identifying characteristics: This moss is an acrocarp, about one inch tall with the characteristic upright growth habit. If you look straight down on a colony, it will look like a patch of darkish green star-bursts. Each leaf has a long white tip or awn which extends about half as far again as the length of the leaf itself. The edges of the leaves are folded over towards the middle. At first this was hard to see, even with magnification, because the two outside edges of the leaf met so closely I could not detect the join. It is easiest to notice just above the base of the leaf where the edges start to fold in. The colony has numerous young sporophytes, each with a bright red stalk and hairy cap pointing skyward. This patch at the Foss Farm also has a large section of male plants, distinguished by the reddish bracts at the tip of the stem, looking like tiny rosettes. The common hair cap moss, Polytrichum commune, shares many of these characteristics but is much taller and doesn't have white awns on the leaf tips.
References: How to Know the Mosses, Elizabeth Marie Dunham, published in 1916, available in the Gleason Library; Illustrated Guide to Some Hornworts, Liverworts and Mosses of Eastern Canada, Robert R. Ireland and Gilda Bellolio-Trucco, 1987, very nice line drawings — available from the Canadian Museum of Nature, Ottawa; Introduction to New England Bryophytes, Mary Lincoln, 2004, with color photographs — available through moss identification classes at the Garden in the Woods in Framingham.
© 2005 The Carlisle Mosquito