Monographs Details: Pireella
Authority: Buck, William R. 1998. Pleurocarpous mosses of the West Indies. Mem. New York Bot. Gard. 82: 1-400.
Scientific Name:Pireella
Description:Genus Description - Plants relatively small to medium-sized or rarely robust, in green to golden, thin to dense, epiphytic colonies. Primary stems creeping, filiform, usually naked or with small, reduced leaves, turning ca. 90° and becoming the upright secondary stem (stipe), the creeping stem continuing by a bud from near the base of the stipe, stipes usually frondose and pinnately branched, rarely simple, erect, sometimes becoming flagellate above with reduced leaves; in cross-section with small thick-walled colored cells surrounding gradually larger mostly firm-walled cells, central strand none; paraphyllia none; pseudoparaphyllia filamentous, numerous; axillary hairs with (1-) 2(-3) short brown basal cells and 2-3 elongate hyaline or rarely brown distal cells. Stipe leaves strongly to slightly differentiated from branch leaves, appressed to squarrose-spreading from a clasping base, ovate-triangular to lanceolate; margins entire to serrulate, plane to recurved; costa single, usually percurrent to subpercurrent, rarely ending near midleaf, sometimes flexuose; cells mostly ± linear, less often oval, smooth or sometimes prorulose, firm- or less often thick-walled, often porose; alar cells often somewhat differentiated. Branch leaves erect to spreading, in 5 obvious spiral rows or not, lanceolate to ovate, broadly acuminate, concave, not plicate, rarely decurrent; margins subentire to serrulate, plane; costa single, usually subpercurrent to percurrent, rarely ending near midleaf, sometimes flexuose, not projecting at apex; cells oval (1.5-3:1) to linear, often prorulose, thin- to thick-walled, sometimes porose, becoming yellow at the insertion; alar cells differentiated in quite small to extensive areas. Asexual propagula often clustered in leaf axils on short stalks, uniseriate. Dioicous, rarely fertile. Perichaetia conspicuous or not; leaves usually strongly differentiated, erect, oblong-lanceolate, abruptly acuminate; margins serrulate above, entire below, plane; costa single, incomplete or absent; cells (where seen) elongate. Setae very short to elongate, smooth or less often roughened, reddish, occasionally flexuose; capsules mostly immersed but occasionally exserted, erect and symmetric, usually broadly oval-cylindric, rarely subglobose; exothecial cells irregularly hexagonal, ca. 1-2:1, thin- to firm-walled; annulus not differentiated; operculum high-conic to short-rostrate; peristome double, inserted below the mouth, prostome often well developed, exostome teeth yellow, not bordered or shouldered, mostly smooth and perforate, not trabeculate at back; endostome strongly reduced to slender short segments, often fragmentary and adherent to the teeth. Spores spherical to ovoid, large, lightly roughened. Calyptrae (reportedly) cucullate or (observed) mitrate, mostly pilose, smooth.

Discussion:Pireella Cardot, Rev. Bryol. 40: 17. 1913; Pirea Cardot in Renauld & Cardot in T. Durand & Pittier, Bull. Soc. Roy. Bot. Belgique 32(1): 175. 1893 [1894], hom. illeg., non T. Durand, Index Gen. Phan. 494. 1888 [Brassicaceae], nec Vavrdová, Vestn. Ustredn. Ustavu Geol. (Praha) 47: 83. 1972 [fossil Acritarcha], hom. illeg. Discussion. Pireella is characterized by mostly well-branched, erect secondary stems arising from a creeping primary stem. The leaves are lanceolate to ovate and the costa usually ends in the acumen. The branch leaves are strongly concave in all species, not plicate as in Pterobryon. The cells vary from oval to linear and the alar cells are scarcely differentiated to quadrate in extensive areas. The plants are dioicous and rarely fertile. The capsules are mostly immersed. The peristome is double but the endostome is strongly reduced and often difficult to demonstrate. The exostome teeth are mostly unomamented and obscured by a well-developed prostome. Arzeni’s (1954: 23-37) treatment of Pireella is flawed by the inclusion of extrageneric taxa and by some erroneous information, but, for the most part, the key does work and the illustrations are helpful. Two of the species that Arzeni included in Pireella, P. cavifolia and P. squarrosa, are here treated in Porotrichodendron and Porotrichum, respectively, as synonyms. More recently, Newton (1993) has monographed Pireella; her conclusions are followed here. I am most hesitant to agree with Newton that Pireella is distinct from Pterobryon, and I am doing so reluctantly.