Species description:
The genus name based on the forked peristome teeth that resemble the horns of an animal. The species name referring to the red­purple seta and the frequently reddish-purple plants.

Reproduction:
Sporophytes common in spring when the deep red setae become conspicuous. Sporangia are glossy red-brown and 16-ribbed when mature, and oriented at right angles to the seta; the immature sporangium is smooth and erector suberect.

Distinguishing characteristics:
The sporophytes are usually present and form the most reliable feature for identification. The inclined, grooved, glossy red-brown sporangium and with a pronounced bulge at its base where it joins the seta, in combination with the dark green or reddish-brown leafy shoots, are characteristic.

Habit:
Forming dense, short turfs varying from dark green to wine-­red, with erect, usually unbranched shoots, stems red-brown; leaves somewhat contorted when dry.

Similar Species:
Although Aulacomnium species possess grooved sporangia, these are light brown and not glossy, and taper gradually into the pale brown seta (dark red-brown in most specimens of Ceratodon). The leafy plants are pale yellow-green in Aulacomnium. Aulaconium androgynum, the species that might be mistaken for Ceratodon, usually grows on wood or humus and gemma-bearing shoots are often present. When without sporophytes Ceratodon can be confused with many gen­era, including Didymodon, Barbula and Bryoerythrophyllum. In these genera, sporangia are erect, cylindric, not grooved when ripe and the peristome teeth are often twisted. Sterile Catoscopium, when moist, show the leaves in three rows, especially near the stem apex, a feature never present in Ceratodon.