Isopterygium cuspidifolium Cardot, Bull. Soc. Bot. Genève, ser. 2, 4: 387. 1912; Plagiothecium mariannae Grout; Taxiphyllum mariannae (Grout) Schornherst

Plants in thin mats, dark green to yellowish. Stems 3 cm, 1-3 mm wide, julaceous to subjulaceous; often radiculose ventrally. Leaves loosely imbricate, ovate to broadly ovate-lanceolate, symmetric, concave, 1-2.5 × 0.5-1 mm; margins plane, serrulate to entire; apex acuminate or filiform-acuminate, often twisted; costa double, short, one branch 1/3-1/2 leaf length, rarely ecostate; alar cells many, quadrate to rectangular, 12-48 × 10-22 µm, in 2-several rows, 5-12 cells in marginal row; laminal cells smooth; medial cells 75-120 × 7-12 µm. Sporophytes unknown.

Calcareous soil and rock, over exposed tree roots; low to moderate elevations (0-300 m); Ala., Fla., Tenn.; Asia.

Taxiphyllum cuspidifolium is distinguished by its julaceous to subjulaceous plants with an oily sheen when moist and by its loosely imbricate, erect-spreading, concave leaves with plane margins and acuminate to filiform-acuminate apices. The species is rare in North America, where it is known from only one locality in Alabama (Bibb County), four in Florida (Alachua, Citrus, Jackson, and Walton counties), and two in Tennessee (Anderson and Montgomery counties). This species has often been confused with Plagiothecium cavifolium (Plagiotheciaceae), which has a more northern distribution. For microscopic differences between the genera Plagiothecium and Taxiphyllum, see the discussion under 2. T. alternans.