The Habitat and Distribution of Meesia triquetra in North America and Greenland

Abstract

Meesia triquetra (Richt.) Aongstr. occurs in rich fens having surface waters with high pH and calcium concentrations. The present day distribution of M. triquetra in North America and Greenland is documented from Alaska and British Columbia east to Newfoundland and Ellesmere Island, N. W. T., and south to northern California in the west and Pennsylvania in the east. A large number of collections have been madefrom the mountains andfoothills in Alaska, British Columbia, and Alberta; also notable are the many collections from the Great Lakes area. All Quaternary subfossil records lie in the same geographic area as extant records except for one station in Iowa and another in southern Ohio, both of which lie south of the present-day range. Meesia triquetra (Richt.) Aongstr. can be distinguished from the other two North American species of Meesia by a distinct three-ranked leaf arrangement, acute leaf apices, denticulate leaf margins, and dioicous sexual condition. Meesia triquetra is a rich fen indicator species of high fidelity. In the boreal region it grows in carpets in open mires, including the flarks of patterned fens and floating mats of pond margins. Meesia triquetra can also be found in hollows of alkaline, swampy Betula and Salix woods. In the Arctic, M. triquetra grows on calcareous seepage slopes and at the bases of hummocks in wet meadows. This moss is considered uncommon and strictly limited in its distribution by habitat availability (Odgaard 1988; Slack et al. 1980). I had opportunity to outline the habitat and distribution of this rare indicator species in North America as part of a larger work on the population biology of M. triquetra. Meesia triquetra usually occurs in fens with high species richness. Among the most abundant moss species found in these fens are Aulacomnium palustre (Hedw.) Schwaegr., Bryum pseudotriquetrum (Hedw.) G.M.S., Drepanocladus revolvens (Sw.) Warnst., D. vernicosus (Mitt.) Warnst., and Tomenthypnum nitens (Hedw.) Loeske. It has also been found as isolated plants in carpets, below lawns of Sphagnum angustifolium (Russ.) C. Jens. and hummocks of S. magellanicum Brid., although this assemblage is rare. When present, M. triquetra can be abundant but is usually found as stems intermingled in carpets of Drepanocladus revolvens (Sw.) Warnst. and Scorpidium scorpioides (Hedw.) Limpr. Other indicator species of these mires are Calliergon triTABLE 1. Chemical parameters of surface waters from fens in which Meesia triquetra occurs.