Weisiopsis oblonga Thér., Rev. Bryol. Lichénol. 5: 95. 1932 [1933].

Protologue: Mexico. Nepantla, sur la terre (St.-P. [Marius Saint-Pierre] n° 1830). 

Plants small, light-green, 1–2 mm high. Stems evenly foliate, not branched, sclerodermis and central strand present; rhizoids sparse, red or hyaline, smooth. Leaves 1.0–1.5 mm long, erect at base, tubulose, incurved when dry, spreading when wet, long-lingulate to spathulate, concave; apices rounded to obtuse, narrowly but deeply grooved along the costa; margins unistratose, plane or incurved, entire to minutely crenulate by projecting cell walls, not bordered; costa subpercurrent, guide cells and single (dorsal) stereid band present, surface cells elongate, ventral surface layer of enlarged, hyaline cells; upper cells rounded-hexagonal to quadrate, 5–9 x 4–10 μm, mammillose-bulging on upper surface, plane to weakly convex, smooth on dorsal surface, basal cells abruptly enlarged, hyaline, 30–50 x 14–20 μm, rectangular, with thin, bulging walls. Autoicous. Perichaetial terminal. Setae 3–6 mm long, yellow. Capsules 0.6–1.2 mm long, ellipsoid to cylindric, smooth, yellow-brown, red at capsule mouth; stomata in neck; opercula 0.3–0.4 mm long, conic-rostrate; annuli of 2–3 rows of vesiculose cells; peristome of 16 red, spiculose, well-spaced, long-linear teeth, inserted within the mouth, to 450 μm long, erect, to slightly twisted, basal membrane absent. Spores 8–10 μm, smooth to lightly roughened. Calyptrae 1.0–1.5 mm long.