Candidate plants of G. incurva may be recognised as small, very dark cushions with very short or non-existent hair-points and erect, narrow leaves. Narrow-leaved muticous forms resemble Hymenoloma crispulum more than a Grimmia.
Like most Grimmia species, confident identification requires cutting transverse leaf sections. If you cut at close to the very top of the leaf, you should get sections through the rounded subula (not the nerve, which ends below the tip) which is composed of homogenous cells, an unusual feature. In the upper part of the leaf, the laminal cells have exterior cell walls that are markedly thicker than the interior walls. Taken together, these are good confirmatory characters for G. incurva.