in W. P. Schimper, Musci Eur. Nov. 1 – 2(1): 1. 1864.
Plants to 4 cm, light green to olive green. Stem leaves stiff, erect-appressed when dry, lanceolate, 2.7–3.6 mm; margins broadly recurved, plane at apex, entire; apex short-acuminate to acute; basal laminal cells elongate, walls thick, nodose; distal cells 9–15 µm, 1-stratose, papillae 2–4 per cell, simple or 2-fid, large. Specialized asexual reproduction absent. Sexual condition gonioautoicous. Seta to 0.4 mm. Capsule immersed to emergent, ovate to cylindric-ovate, 1.6–1.8 mm, usually smooth or slightly 8-ribbed when dry; stomata superficial; peristome usually single; prostome small or absent; exostome teeth 16, recurved, coarsely papillose to papillose-striate; endostome rarely present, segments 8, rudimentary, of 1 row of cells, smooth. Calyptra oblong-conic, smooth, hairy, hairs papillose. Spores 14–17(–20) µm.
Habitat: Tree trunks
Elevation: elevation unknown
Orthotrichum shawii is similar to O. rupestre but distinguished by the 16 short, recurved exostome teeth and nearly smooth capsules, while O. rupestre has erect or spreading exostome teeth and variable capsule ribbing. Orthotrichum shawii was collected in California once without exact locality in the 1860s (Bolander 481780, NY). Stomata are found in the mid and distal capsule, the exostome teeth are irregularly divided, and the endostome segments are very short and hyaline.