Ceratodon Bridel, Spec. Musc. 126. 1801.
Greek cerat, horn, and odon, tooth.
Terry T. McIntosh
Plants in loose to dense tufts, turfs, or mats, green to dark green, brownish-green, light green or yellow-green, usually darker below, often tinged reddish brown or purple. Stems (0.2--)1--3(--4) cm, erect, mostly simple, usually branched, central strand present, rhizoids at base, papillose. Leaves erectopatent to contorted or somewhat crisped, rarely straight when dry, sometimes forming a comal tuft, patent to erectopatent to spreading when wet, lanceolate, ovate-lanceolate, or triangular-lanceolate, to elliptical to ovate and somewhat concave, distal leaves 0.35--2.8 mm, proximal somewhat shorter, margins recurved to near apex or rarely plane, irregularly serrate to uneven or smooth distally, plane and entire proximally, apices acute to short-acuminate or rarely obtuse, nondecurrent; costa strong, sub-percurrent to excurrent, sometimes as a long, smooth awn, prominent on abaxial surface, 1 row of guide cells, two well-developed stereid bands, hydroid cells present between guide cells and abaxial stereids, adaxial surficial cells elongate-rectangular, much longer than laminal cells; medial laminal cells of somewhat uneven shape and size across leaf, more or less quadrate to short-rectangular, often irregularly angled or rarely rounded, (6.5--)8--12(--22) µm, often longer at leaf apex and base, especially adjacent to the costa, up to 25 µm long, smooth, non-pitted, cell walls even, usually of medium thickness, somewhat thicker and often rounded at the cell angles, alar cells lacking. Specialized asexual reproduction lacking or as multicellular filamentous propagules with thin walls scattered along the stems or occasionally as rhizome nodules. Sexual condition dioicous; male and female plants about the same size; perigonial leaves ovate, concave, short-acuminate or rarely long-acuminate in well-developed plants; perichaetial leaves convolute-sheathing, abruptly subulate to gradually acuminate. Seta solitary, red to purplish to yellow or yellow-orange, (0.5--)1.5--3(--4) cm, arising from apex of stem, smooth, erect, twisted when dry. Capsule erect to inclined or horizontal, dark red to reddish or purplish brown, to pale brown, pale yellow or yellow-orange, oblong-ovoid to oblong-cylindric or cylindric, often somewhat asymmetric and deeply furrowed, (1--)2--2.5(--3) mm, smooth to strongly sulcate when dry, usually strumose; annulus of 2--3 rows of large, deciduous, revoluble cells; operculum conic to long-conic, straight; peristome single, consisting of 16 teeth and basal membrane, split nearly to their base into 2 filiform segments free to united at their nodes basally, 5--18 articulations, finely papillose to spinulose-papillose, dark red and bordered to completely pale and lacking borders. Calyptra fugacious, cucullate, light green to yellowish with a reddish tip, smooth, naked, covering most of capsule. Spores globose, 10--15 (--22) µm, smooth to finely papillose, yellow, sometimes greenish.
Species 3 (2 in the flora): worldwide.
Historically, Ceratodon has been a troubling genus. Taxonomic interpretations, especially with respect to C. purpureus sens. lat., 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) provide the most thorough treatment of Ceratodon to date, reducing the number of species to four and sub-species of C. purpureus to three. One of their species, Ceratodon conicus, is treated here as a sub-species 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.
Burley, J. S. and N. M. Pritchard. 1990. Revision of the genus Ceratodon (Bryophyta). Harvard Papers in Botany 2: 17--76. Crum, H. A. and L. E. Anderson. 1981. Mosses of Eastern North America. Vol. 1. New York. Flowers, S. 1973. Mosses: Utah and the West. Provo, Utah. Grout, A. J. 1936. Moss Flora of North America North of Mexico. Vol. 1. Newfane, Vermont. Ireland, R. R. 1982. Moss Flora of the Maritime Provinces. National Museums of Canada, Nat. Mus. Nat. Sciences, Publs. in Botany 13. Ottawa. Lawton. E. 1971. Moss Flora of the Pacific Northwest. Hattori Botanical Laboratory, Nichinan, Japan. Nyholm, E. 1986. Illustrated Flora of Nordic Mosses. Odense. Snider, J. A. 1994. Ceratodon. In: Sharp, A.J., H. Crum and P.M. Eckel, eds. The Moss Flora of Mexico. Mem. New York Bot. Gard. 69: 103--105. Steere, W. C. 1978. The Mosses of Arctic Alaska. Vaduz, Liechtenstein.