Definitions

percurrent

Meesia triquetra

Threeranked humpmoss (Meesia triquetra), is a moss that occurs all around the northern hemisphere in higher latitudes.

Technical description

In small tufts or cushions. Plants acrocarpous, dioicous, often large, dark-green to grass-green above, occasionally red-brown below due to dense rhizoids. Stems not or little branched, pale-brown to yellow-brown, closely foliate, 2–14 cm high. Leaves decurrent, squarrose (spreading) when moist, triangular to ovate to lanceolate, somewhat crispate (contorted), 2–3½ mm long, tristichous (in three obvious ranks); margins sharply serrate or denticulate to the base or nearly so, plane or sometimes recurved in the middle of the leaf; costa relatively narrow (less than 1/5 the width of the leaf base), subpercurrent to percurrent, gradually tapering at distal end; apex acute to acuminate (sharply pointed); lamina unistratose throughout. Perigonia terminal in discoid heads. Seta straight and smooth, brown to yellow-brown, very long (4–10 cm). Capsule asymmetrical, somewhat pyriform, 2¾–5½ mm long including the neck; hypophysis (neck) long (comprising up to ½ of capsule length), moderately well-defined, not much wrinkled when dry; urn oblong to short-cylindric, arcuate and asymmetric, brown to yellow-brown, to 4 mm long, when dry wrinkled but not regularly sulcate; operculum short-conic; endostome cilia often rather well-developed. Spores finely papillose.

Distribution, habitat, and ecology

This species has a circumboreal distribution: it is found in Northern Europe, northern Asia, Greenland, Canada, and the northern U.S. Some discoveries have been reported from Oceania.

These mosses occur in wetland sites, specifically, within wet woods in the wettest portions of what are called "extreme rich fens" (i.e., fens having surface waters with high pH and calcium concentrations). Montagnes describes this species as a "rich fen indicator of high fidelity." Associates include Scorpidium spp. and Drepanocladus revolvens.

The fire ecology of this plant is not known; however, fens rarely burn. Excess soot from a nearby fire, however, might negatively affect habitat quality. Fire return intervals in conifer bogs, a somewhat similar mire-type habitat, are estimated to be about once every 150-200 years. Fire does significant damage to peat, but the bog must be dry (as during a drought year) in order to burn; typically, bogs are not dry enough.

Conservation status and threats

U.S. Forest Service Pacific Southwest Region Sensitive Species.

California Native Plant Society List 4.2

NatureServe California State Rank: S2.2; Global Rank: G5

Fens are delicate habitats susceptible to impacts from livestock grazing, hydrologic alteration, construction and continued use of roads, and peat mining. Rich fen habitats are especially susceptible to modification. The surface water chemistry of rich fens is sensitive to climatic and anthropogenic influences. This species has reached near extinction in Europe.

Field identification

M. triquetra is easily recognized by its distinct three-ranked leaf arrangement and for being dioicous. It may be distinguished from M. uliginosa by: its squarrose leaves; its narrow costa relative to the size of the leaf base; its serrate, planar leaf margins; and acute leaf tips; these as opposed to the wide (up to 1/3 of the leaf base) costa, the entire, revolute leaf margins, and the blunt apices of M. uliginosa; other Meesia species also have blunt apices..

References

External links

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