Plants ca. 0-5--1.5 cm ´ 1.5--2 mm, prostrate-ascending, green-brownish. Stems 0.33--0.35 mm in diam., sparsely branching, transverse section with 1--2 cortical cells and 12--16 medullary cells; rhizoids numerous, colorless. Leaves succubous, imbricate, canaliculate, ovate-oblong, 0.7--1 ´ 0.6--0.8 mm, unequally 3-lobed (occasionally 2--4-lobed); lobes acute to subacute, sinus between lobes shallow (0.2--0.3 of the leaf length), apex rounded to truncated, margins entire; cells subquadrate, marginal cells 16--22 ´ 24--30 m m, median cells 22--28 ´ 26--36 m m, basal cells 25--30 ´ 35--55 m m, cuticle verruculose, walls thin, trigones large (weakly bulging); oil bodies 4--10 per cell, spherical to ovoid, 5--8 ´ 5--10 m m, papillose; underleaves absent. Specialized asexual reproduction by gemmae in masses at apices of shoots and tips of leaf lobes, reddish-brown, polygonal, 16--24 ´ 20--30 ´ 15--25 m m, 1--2-celled, smooth. Sexual condition dioicous. Androecia terminal, male bracts similar to leaves, 2-androus, antheridial stalk 1-seriate. Gynoecia terminal, female bracts larger than leaves, broadly oblong, 3--4-lobed with acute sinuses. Perianths cylindrical, 4--5- plicate, mouth ciliated with teeth 2--5 cells long. Capsule ovoid, wall 4-stratose, both outer and interior walls with nodular thickenings, yellowish-brown. Elaters ca. 9 m m in diam., 2-spiral, brownish. Spores 14--16 m m, papillose, brownish.

With other bryophytes on calcareous soil and decayed wood; 0--3500 m; e, w, nw Greenland; Alta., B.C., N.B., N.W.T., Nun., Que., Yukon; Alaska, Mich., Minn., Mont., Wis.; Europe.

The sporophyte of this species is very rare. Tritomaria scitula is frequently associated with Anastrophyllum minutum, Barbilophozia binsteadii, B. floerkei, B. lycopodioides, B. quadriloba, Blepharostoma trichophyllum subsp. brevirete, Cephalozia pleniceps, Jungermannia sphaerocarpa, Leiocolea heterocolpos, Odontoschisma macounii, Plagiochila asplenioides, Tritomaria exsectiformis, T. quinquidentata, Scapania cuspiduligera, and S. mucronata.