T. tasmanicum is a dark, cushion-forming aquatic to semi-aquatic moss which typically occurs near waterfalls or on stones in rivers and stream banks. The shoots range from 2-7 cm high, bearing dark olive green leaves. The tongue shaped leaves are hooded near the apex. The single nerve ends at the apex or just below. When dry the leaves curve inwards at the tips or are sometimes cockscrewed.

T. tasmanicum may be mistaken for Racomitrium crispulum but the tongue-shaped leaves with hood-shaped apices of the former is a good distinguishing character.

T. tasmanicum was previously included under the Pottiaceae.