Until some years ago the genus Isothecium together with the genus Plasteurhynchium was subordinated to the family Lembophyllaceae (Neckerales), but now is contained in the family Brachytheciaceae because of its similarity to Brachythecium. The only difference between Isothecium species and Brachythecium species are the quadratic, thick walled, not inflated alar cells.
The pricipal stems of the mosses of this genus are in mostly decumbent and fixed with rhizoids in the ground, the branches are ascending and pending, and often dendroid. They are swollen foliated.
The leaves have long rhombic until prosenchymatic cells. The midrib approximately reaches the mid of the leaf. The edge of the leaf is at least in the upper part serrulate.
The genus consists of about 15 species in the moderate latitudes of the northern hemisphere. Three of them can be found in Europe, and two in germany. They grow on rocks or on trunks of trees.
Isothecium alopecuroides, the species on the picture, has about 2-3mm long leaves, which are only indistincly serrulate at the upper part. They are broad ovoid and only short apiculate. The branches are only indistinctly dendroid. Sometimes they are somewhat bushy ramified in the upper part. They are ascending and pendant. The species grows on trees or on rocks in forests.