Bryol. Univ.1: 480. 1826 ,
Species 3 (2 in the flora).
Historically, Ceratodon has been a troubling genus. Taxonomic interpretations, especially with respect to C. purpureus in the broad sense, have varied widely, mainly because of the high degree of environmental and suspected genetic variation across its range. J. S. Burley and N. M. Pritchard (1990) provided the most thorough treatment of Ceratodon to date, reducing the number of species to four and subspecies of C. purpureus to three. One of their species, C. conicus, is treated here as a subspecies of C. purpureus, based on the apparent gradation and reduction of all of the characters that they used in their treatment. However, there remains a great need for a detailed study of this genus within North America.
|1||Vegetative leaves elliptic to ovate-lanceolate, concave, obtuse; distal laminal cells usually 12-16 mm, sometimes longer; leaf margins plane to weakly recurved and usually entire; most costa sub-percurrent; capsule ovate to ovate-cylindrical, about 1 mm; spores usually19-21 µm; restricted to Arctic regions.||Ceratodon heterophyllus|
|1||Vegetative leaves usually lanceolate to ovate-lanceolate, acute to short-acuminate; distal laminal cells usually 8-12 mm; leaf margins recurved and usually toothed distally; costa percurrent to long-excurrent; capsule ovate-cylindrical to cylindrical, usually longer, to 3 mm; spores usually 11-14 µm; widespread.||Ceratodon purpureus|