3. Coscinodon Sprengel, Anleit. Kenntn. Gew. 3: 281. 1804.
[Greek koskinon, sieve, and odon, tooth, alluding to peristome]
Roxanne I. Hastings
Plants 4.5-15 mm, in dense cushions to loose mats, olivaceous to dark black-green. Leaves oval to ovate-lanceolate, keeled distally, margins plane, incurved, or recurved, distal lamina 1- or 2-stratose, specialized laminal and marginal chlorophyllose structures absent, usually long-awned; basal cells usually rectangular with straight walls; mid leaf and distal cells quadrate to short rectangular, straight or sinuose, usually thick-walled. Gemmae absent. Sexual condition autoicous or dioicous; perichaetial leaves enlarged. Seta short to long, straight. Capsule erect, immersed to exserted, symmetric, campanulate, ovoid to cylindrical, rarely cupulate; annulus poorly differentiated; operculum conic to rostrate, falling detached from the columella. Calyptra campanulate, becoming cucullate with age, erose at base, large, covering 1/2 to all of capsule, plicate.
Species 10 (5 in the flora): North America, South America, Eurasia.
Species of Coscinodon are widespread across North America but are largely absent from the interior Great Plains and along the west coast. They all prefer dry acidic rocks. The largely calcareous regions of the continental interior do not provide suitable habitat for these species. Historically, North American authors have often considered Coscinodon to be a subgenus of Grimmia. Not until the 1980s did they follow the European approach distinguishing the two genera, the separation of which is based largely on the sporophyte. Coscinodon have large, campanulate, plicate calyptrae that commonly cover the capsule, whereas Grimmia have smaller, non-plicate calyptrae that are not campanulate. It is often stated that Coscinodon have very long awns compared to most Grimmia. This is true for the widespread species, C. calyptratus and C. cribrosus, and also C. yukonensis. But C. arctolimnius is muticous to short-awned and C. hartzii has awns not much longer than those of most Grimmia.
Hastings, R. I. 1999. Taxonomy and biogeography of the genus Coscinodon (Bryopsida, Grimmiaceae) in North America, including a new species. Bryologist 102: 265-286.