The specific epithet was applied by Hedwig because he recognized the many differences that separate the species from T . Thuidium allenii C. F. Austin, Bull. Plants slender, light-green or yellow. Stems and branches loosely foliate. Stem leaves erect-spreading when moist, loosely erect or slightly incurved when dry, ca.
Branch leaves ending in a truncate, pluripapillose cell.
Perichaetial leaves eciliate. Seta 25-30 mm long. Va. Thuidium allenii is slender and loosely, sometimes irregularly bipinnate. It could easily be taken for a depauperate expression of Thuidium delicatulum . However, it is smaller and has short-pointed stem leaves with margins plane or nearly so and noticeably incurved branch leaves.