Stem leaves patent-erect, spreading, concave, occasionally plicate, lamina 2-stratose distally (appearing multistratose in extreme forms), 1-stratose at base; proximal leaves ovate to deltoid, long-acuminate, 0.18--1.1 × 0.1--0.28 mm, entire proximally, serrulate distally; distal stem leaves deltoid to ovate, long-acuminate, 0.58--1.88 × 0.15--0.35 mm, entire proximally, serrulate distally along the margin of the acumen to serrate with anteriorly projecting cell ends on the abaxial surface of costa; costa broad, percurrent. Perichaetial leaves with oblong-ovate to lanceolate base, gradually to abruptly narrowed to a subulate to acuminate tip, 1.25--4.3 × 0.25--0.5 mm, margins entire proximally, plane to incurved, entire to irregularly serrulate distally especially along margin of acumen, marginal cells short-rectangular to quadrate; basal cells loosely rectangular to quadrate; median cells subquadrate to rectangular to trapezoidal; distal cells in acumen linear; costa percurrent, indistinctly defined, filling the cucullate acumen; transverse section of costa at mid leaf showing a row of central guide cells confluent with the adaxial laminal cells, a widespread abaxial band of stereids, a restricted adaxial group of stereids, and a few thin-walled accessory cells in the center; innermost perichaetial leaves long-lanceolate with an acuminate tip, percurrent, 1.13--2.6 × 0.11--0.25 mm. Specialized asexual reproduction reportedly by rhizoidal tubers. Sexual condition paroicous, 1--2(--3) antheridia naked or subtended by 1(--2) bracts in the distal leaf axils proximal to the perichaetium, generally in 1--2 leaf axils per stem. Seta 0.075--0.5 mm. Spores 20--30(--35) µm, densely papillose, light orange-brown in mass.

Tufts on open disturbed soil, old fields, along railways and roads on sandy banks; B.C.; Ala., Ark., Calif., Ga., Kans., La., Mass., Md., Mo., N.C., Okla., Ohio, Oreg., Pa., Md., N.Y., Va., Wash., W.Va.); Europe; s Africa, Atlantic Islands, Pacific Islands (New Zealand), Asia (China).

This species is reported for China by P.-S. Xu 1989). The chromosome number is n = 26 (Bryan 1956; Crum & Anderson 1981). Pleuridium acuminatum is characterized by (1) the paroicous sexual condition and (2) the 2-stratose leaf lamina at shoulder. The bolanderi- and the stramineum-expressions represent intermediate variations between the common variant of P. acuminatum (with a sporadically 2-stratose lamina) and the californicum-expression (almost completely 2-stratose). W. C. Steere et al. (1954) and V. S. Bryan (1956) have pointed out that the n = 26 chromosome count in the bolanderi-expression provides evidence for its conspecificity with P. acuminatum. The stramineum-, bakeri- and elongatum-expressions have long been treated as taxonomic synonyms of the bolanderi-expression (L. E. Anderson et al. 1990; E. G. Britton 1913; H. A. Crum et al. 1973; A. J. Grout 1936; E. Lawton 1971).