The monotypical genus Dryptodon with its only species Dryptodon patens in a certain manner is an intermediate genus between the two big genera Grimmia and Racomitrium. Its habit is similar to some forms of Racomitrium, whose leaves are without hyaline hair. But the cell walls are, at least in the lower part of the leaves, only very little knottily thickened.
The peristome is similar to the peristome of Racomitrium (with teeth devided to the base), but the seta is arcuate as in many Grimmia species, but none of the Racomitrium species.
As a consequence the species is sometimes called Grimmia patens (Hedw.)BSG, and sometimes
In total it is rather easy to recognize: On the dorsal side of the midrib there are 2, sometimes 4 furrows, which can even be guessed on the picture. The other characteristics are not very noticeable: The leaves are long lanceolate and without hyaline hair. The cells in the lower part of the leaf are long rectangular, in the upper part quadratic or broader than long. The plants form dense and dark green cushions, which are in most cases about 5cm high, sometimes until 10cm.
The species grows in chalkfree stone in the mountains. In central Europe it is rare and is only more frequent locally at some places in the mountains. In parts of germany it is extinct. The specimen on the picture comes from Iceland.