Leaves ovate to oblong-lanceolate, apex broadly acute to rounded, mucronate to short-awned, margins revolute in mid 2/3--3/4 of leaf, weakly bordered from apex to near base with (2--)4 rows of weakly thicker-walled and less-papillose or smooth cells; costa excurrent, lacking an adaxial pad of cells though convex adaxially, distally narrow, 3--4 cells across adaxial surface; distal laminal cells subquadrate to hexagonal, occasionally somewhat elongated longitudinally, width 13--18 µm wide, 1(--2):1, papillose with 4(--6) simple papillae per lumen. Sexual condition autoicous. Sporophytes exerted. Seta length 0.2--0.4 cm. Capsules stegocarpic, not systylius, broadly cylindric, erect and nearly straight, urn ca. 1.4--1.5 mm; peristome remaining adherent to the inside of the operculum, teeth rudimentary to linear, to 300 µm, of several filaments variously anastomosing and weakly twisted, basal membrane length to 50 µm; operculum ca. 0.7--0.8 mm, not falling. Spores ca. 20--25 µm, spheric, densely low-papillose.

Capsules mature winter--spring. Soil; low elevations; Sask.; Ariz., Calif., Colo., Minn.; Mexico (Baja California); Europe; sw Asia.

In Tortula protobryoides, only by dissecting the capsule can the peristome be revealed as it is attached to the inside of the operculum. The capsule boasts an annulus but the operculum does not fall. The peristome adherent to the operculum is scarcely unique in the Pottiaceae. A peristomate capsule with operculum differentiated but not falling is matched in at least some specimens of Microbryum starckeanum var. fosbergii. In T. cernua, the peristome is attached and the operculum falls, taking the peristome with it. The gametophyte of T. protobryoides is similar to that of Tortula acaulon and T. lanceola but the papillae are more dense. The perigonia are borne at the ends of short, basal branches.