Plants with deciduous, longer distal leaves with a less well-developed sheath. Leaf apex acute or acuminate; costae ending a few cells below apex or excurrent; sheath clear in the distal leaves, orange-brown to reddish black in the proximal leaves; limb green, pellucid; limb-sheath transition gradual; limb margins coarsely dentate in distal 1/3-1/2, slightly toothed, crenulate or ± entire proximally; limb lamina cells 6-16(-18) × 6-14 µm, with tall rounded mamillae on the adaxial surface, abaxial surface smooth; sheath lamina cells with (0-)1-6(-8) large round, verrucose papillae over abaxial surface of the lumen; cells at leaf insertion abruptly differentiated into 1 to a few rows of fragile, hyaline cells; limb costa papillose on abaxial surface, or toothed near the apex, adaxial cells with tall bottle-shaped mamillae. Sexual condition dioicous; perichaetial leaves longer and more evenly tapering than stem leaves, sheath poorly developed. Calyptra unknown. Capsule non-plicate; exothecial cells with extremely sinuose walls; stomata on neck and proximal urn; endostome cilia with numerous short blunt appendiculations on the interior surfaces. Timmia norvegica is related to T. sibirica, with which it shares the important character of fragile leaf bases; however, the papillosity of the limb in T. sibirica is a strongly differentiating character. Timmia norvegica differs from T. austriaca and T. megapolitana by having fragile leaf bases, heterophyllous leaves, and less well delimited leaf sheaths.
