13. PLEUROCHAETE Plate 16.

Pleurochaete Lindb., Oefv. K. Vet. Ak. Foerh. 21: 253, 1864. Type: Pleurochaete squarrosa (Brid.) Lindb.

Barbula subg. Pleurochaete (Lindb.) Schimp., Syn. ed. 2: 220, 1876.

Tortella subg. Pleurochaete (Lindb.) Limpr., Laubm. Deutschl. 1: 607, 1890.

Barbula sect. Pleurochaete (Lindb.) C. Müll., Linnaea 39: 400, 1875.

Barbula sect. Squarrosae Lesq. & James, Man. N. Am. Moss. 130, 1884, nom. illeg. incl. sect. prior. Type: Barbula squarrosa Brid.

Barbula sect. Squarrosa Lzaro é Ibiza, Bot. Descr. Comp. Fl. Esp. 1: 586, 1896, nom. illeg. incl. Barbula sect. Pleurochaete (Lindb.) C. Müll. Type: Barbula squarrosa Brid.

Barbula subsect. Squarrosae C. Müll., Linnaea 39: 402, 1875.

Plants forming a deep or sprawling turf, green above, brown below. Stems branching irregularly, to 4.0 cm in length, transverse section rounded-pentagonal, central strand small, walls of central cylinder cells thin to weakly thickened, sclerodermis of 2–4 rows thick-walled cells, hyalodermis present; axillary hairs to 15 cells in length, cells all hyaline; indumentum weakly radiculose. Leaves spreading and strongly contorted when dry, squarrose-recurved above a sheathing base when moist, oblong-lanceolate, 3–5 mm in length, upper lamina broadly channeled, margins plane but occasionally recurved to revolute along leaf base, denticulate in upper 1/3 of leaf to throughout, 1–2 marginal rows often weakly papillose distally beyond a border of hyaline, thin-walled rhomboidal cells not merging below with inner basal cells but instead extending as a distinct hyaline strip to leaf insertion, 4–7 cells in width below, narrowing upwards, reaching barely higher than shoulder of leaf base to 3/4 leaf length; apex usually sharply acute, occasionally broadly acute; base ovate to rectangular, often broadly sheathing and with distinct shoulders; costa short-excurrent as a sharp mucro, superficial cells quadrate to short-rectangular and papillose from top of sheathing leaf base to near apex ventrally, elongate and smooth dorsally, 6–8 rows of cells across costa ventrally at midleaf, costal transverse section semicircular or reniform, stereid bands strong ventrally and dorsally, larger dorsally, epidermis differentiated in one layer ventrally, present or absent dorsally, guide cells 4–6 in 1 layer, hydroid strand absent; upper laminal cells subquadrate, 8–11 µm in width, 1(–2):1, walls thin or evenly weakly thickened, superficially bulging on both exposed sides or only ventrally and then weakly convex dorsally; papillae bifid, 1–4 per lumen; basal cells differentiated and rising higher medially, distinct from the 4–6 rows of border cells, rectangular to rhomboidal, 10–20 µm in width, 2–5:1, walls thin to evenly thickened or porose. Dioicous. Perichaetia on very short lateral branches, inner leaves long-lanceolate, narrower than cauline leaves, to 5 mm in length, sheathing the seta, lower cells rhomboidal to rectangular and porose, reaching to 3/4 length of inner leaves. Perigonia lateral on the stem, small. Seta 1.3–1.7 cm in length, 1 per perichaetium, orangish to reddish brown, twisted clockwise; theca 2.0–2.8 mm in length, light yellowish or reddish brown, cylindrical, exothecial cells rectangular to rhomboidal, 20–25 µm in width, 3–4:1, walls thin, stomates phaneropore, at base of theca, annulus of 3–5 rows of vesiculose cells, persistent; peristome teeth 32, filamentous, branched spiculose, 300–1000 µm in length, often broken, with several articulations, twisted once counterclockwise, basal membrane apparently absent or to 35 µm high in height, low-spiculose. Operculum long-conic, 0.9–1.7 mm in length, cells twisted counterclockwise. Calyptra cucullate, smooth, ca. 4 mm in length. Spores 10–13 µm in diameter, yellowish brown, papillose. Laminal KOH color reaction deep yellow to orange. Reported chromosome number n = 13.

Found in dry areas on soil and rock (generally calcareous), occasionally on tree roots; North, Central and South America, Europe, North and Central Africa, the Middle East and Asia.

Crum and Anderson (1981) pointed out that Pleurochaete is quite like Tortella in several respects but differs in that the differentiated thin-walled marginal cells, which extend up from the insertion often to above midleaf, do not form a coherent basal vee extending medially to the costa (Pl. 16, f. 7, 14). The inner basal cells, instead, form a distinct region, much as in the case with some but not all Pseudosymblepharis species. Pleurochaete is much like the Asian Chionoloma in leaf shape, marginal strip of elongate cells (Pl. 16, f. 13), and upper medial cells often bulging much greater ventrally than dorsally, but the latter has thick-walled border cells and the upper laminal margins are sharply incurved as in Weissia.

Variation in the degree of extension of the basal marginal cells up the leaf margins and in the length of the inner basal cells is not quite continuous, but is correlated with plant stature. Pleurochaete squarrosa has a largely Temperate Zone and paleotropical facies (P. squarrosa s. str., found in Europe, Ethiopia, the Congo, southern U.S.A., Mexico) and a neotropical facies (P. luteola, found in southeastern U.S.A., e.g. Tennessee, Zander 4333, BUF, and Arkansas, Crum & Anderson's exsiccat Mosses of North America 951 as P. squarrosa; and Latin America). These morphotypes are distinguishable in most specimens examined. Crum and Anderson (1981), however, felt that the neotropical variant is only a “robust expression,” not worthy of a separate name; Crum (1951) indicated that, where growing sympatrically, these may sometimes be difficult to name as one or the other. In any case, a varietal name is provided here for workers like myself who wish to distinguish among the two. The var. luteola (Pl. 16, f. 11–16) differs in being more robust, with a more highly sheathing leaf base, and the border of thin-walled marginal cells being strongly denticulate and extending farther up the leaf margins. This parallels the distinction between Molendoa hornschuchiana and M. sendtneriana, the former differing in stature (largest in the genus) and denticulate lower leaf margins; however, the larger species of Molendoa is distributed primarily across the Alps and Himalayas (one station is in Alaska), while the latter ranges from the Andes and North American Cordillera across the Arctic and throughout the Eurasian continent in arctic-montane situations. Thus, if the each of these two genera developed intraspecifically through reduction, then Pleurochaete probably originated in Gondwanaland and Molendoa is Laurasian, but vice versa if large stature and marginal denticulation are elaborations.

African material identified as Pleurochaete beccarii at BM and NY is P. squarrosa var. squarrosa; type material of P. beccarii at TR could not be obtained on loan but is probably also synonymous. Pleurochaete malacophylla is doubtfully distinct from P. squarrosa var. squarrosa.

Additional literature: Nebel (1990), Quarterman (1956), Wyatt and Stoneburner (1982).

Number of accepted species: 4.

Species examined: P. malacophylla (BM), P. squarrosa.

New combinations and statuses: Pleurochaete squarrosa (Brid.) Lindb. var. luteola (Besch.) Zand., comb. et stat. nov. (Trichostomum luteolum Besch., Mém. Soc. Sc. Nat. Cherbourg 16: 178, 1872; Pleurochaete luteola (Besch.) Thér.).