Rev. Bryol. 40: 17. 1913.
Plants 0.2–10 cm, dark green to yellowish, dull to glossy. Stems with short or long stipelike basal region, simple or irregularly pinnate. Stem leaves obscurely seriate, erect when dry, spreading when moist, broadly ovate-acuminate or ovate-lanceolate, not plicate; base auriculate, decurrent, or not; margins plane; costa single, short in proximal leaves, percurrent or short-excurrent in distal leaves; alar cells little differentiated or in several rows along margin, rectangular or quadrate; medial laminal cells sinuate, prorate, walls porose. Branch leaves differentiated from stem leaves, weakly or strongly seriate in 5 rows, spreading when dry or moist, not plicate; apex flat, acuminate; costa percurrent; medial laminal cells sinuate, weakly or strongly prorate. Seta 0.5–1.2 cm. Capsule cylindric; operculum rounded or conic, rostrate. Calyptra covering capsule, smooth, hairy.
se United States, Mexico, West Indies, Central America, n, c South America.
Species 13 (2 in the flora).
Pireella is the largest genus of Pterobryaceae in the Neotropics, and is composed of three distinct groups; two are not represented in the flora area and are not covered by the description above. The two species in the flora area are rather similar and frequently have been misidentified in the past; they differ in the shape of the leaf base, the number, size, and distribution of alar cells, the shape and stance of the leaves, and the branching pattern. The leaf base characters are most useful, but can be distinguished reliably only by the distal stipe or stem leaves. There are many misidentifications in exsiccatae issued by W. Bauer and by A. J. Grout, and material annotated by C. B. Arzeni and by E. Britton. Distributions of the species differ in the flora area; elsewhere, their ranges overlap.
|1||Stems branched; branch leaves weakly seriate; distal stipe leaf bases often auriculate, weakly to strongly rounded, not decurrent; alar cells indistinct or (especially in auriculate plants) in 1 or 2 rows of few cells, irregular-quadrate, not reaching margin.||Pireella pohlii|
|1||Stems simple or sparsely branched; branch leaves strongly seriate; distal stipe leaf bases not auriculate or rounded, decurrent; alar cells in 7-14 rows of 2-23 cells, quadrate or short- rectangular, into decurrent wing and along margin.||Pireella cymbifolia|