Grimmia teretinervis

Plants in loose tufts, green-brown to reddish brown, shiny. Stems 2-3 cm, central strand strong. Leaves ovate-cordate to lanceolate, 0.6-1.2 × 0.2-0.5 mm, keeled, not plicate, margins plane, awn to 0.3 mm, often just hyaline tipped, commonly long-decurrent, costal transverse section prominent, circular distally; basal juxtacostal laminal cells quadrate to short-rectangular, straight, thin- to thick-walled; basal marginal laminal cells oblate to quadrate, straight, thick-walled, not hyaline; medial laminal cells rounded-quadrate, thick-walled; distal laminal cells 2-stratose, bulging, marginal cells 2-stratose, bulging. Sexual condition dioicous, perichaetial leaves unknown. Seta unknown. Capsule unknown.

Moist calcareous sandstone, limestone and dolomite outcrops; moderate to high elevations (200-1700 m); Alta., B.C., N.W.T., Ont., Que., Sask., Yukon; Alaska, Ark., Colo., Minn., Mo., Mont., Nev., Okla., Wis.; Europe.

As reported by R. R. Ireland (1982b), Grimmia teretinervis is widely scattered across North America, but nowhere is it common. R. I. Hastings (2002) added several more Western collection locations to those reported by Ireland. Based on field observations and by correlating collecting localities with bedrock geology, Hastings proposed that the distribution of G. teretinervis in North America is largely correlated with the boundaries of ancient epicontinental seaways. These deposits have subsequently undergone faulting or were subjected to glacial-fluvial erosion. The ancient oceans provided the calcareous sediments, and the faulting and erosion created the steep exposures preferred by G. teretinervis. Sporophytes have never been observed for this species and, until reported by Ireland, antheridial plants also were unknown. Despite the lack of sporophytes, this species is readily identified by its unique costal structure, which is circular in transverse section. It commonly has thick-walled, bulging laminal cells and very short awns that are none-the-less often long-decurrent. These features give the plants a blackish brown, shiny thread-like appearance.