I. attenuata is an uncommon subalpine rock or soil dwelling species. Plants are black or dark brown in color. The leaves are inserted onto the stem transversely and are distinctively narrow and bifid (with two lobes) to more than halway. Under a light microscope, the lobes appear papillose. The underleaves are almost the same size as the leaves. Oil bodies occur at a frequency of 1-4, are colorless or grey and smooth or moderately granular.