22. TRIQUETRELLA Plates 28– 29.

Triquetrella C. Müll., Öst. Bot. Zeit. 47: 421, 1897. Lectotype: Triquetrella tristicha (C. Müll.) C. Müll. fide Grout, Moss Fl. N. Amer. 1: 170, 1938.

Plants growing in mats, yellowish or blackish green above, brown or blackish brown below. Stems branching occasionally, to 7 cm in length, transverse section rounded-triangular, central strand absent or present and small, sclerodermis present, of 1–3 layers of stereid cells, hyalodermis absent; axillary hairs to 9 cells in length with cells weakly bulging, basal 1–2 cells thick-walled; weakly radiculose below. Leaves in 3 distinct rows, the rows straight or weakly spiralling in either direction, appressed- to spreading-incurved when dry, widely spreading to squarrose and strongly reflexed when moist, triangular to ovate-triangular, ca. 2 mm in length, upper lamina keeled, narrowly channeled along costa, margins recurved in middle 3/4–4/5 of leaf, entire to weakly serrulate near apex; apex narrowly acute to short-acuminate; base ovate, basal leaf margins broadly long-decurrent; costa percurrent, superficial cells elongate and weakly papillose ventrally, rhombic-quadrate near apex and papillose dorsally, 2(–4) rows of cells across costa ventrally at midleaf, costal transverse section ovate to semicircular, 2 stereid bands present, ventral epidermis absent, the dorsal weakly differentiated, guide cells 2–4 in 1 layer, hydroid strand absent; upper laminal cells rounded rhombic to quadrate, ca. 9–11 µm in width, 1:1, occasionally elongate transversely, walls thickened, weakly trigonous, superficially weakly convex to distinctly bulging on both sides; papillae spiculose, mostly simple to bifid, 1 per lumen; basal cells differentiated weakly in a very small group medially, occasionally across insertion, rectangular, little wider than upper cells, 2–4:1, walls thick-walled, somewhat porose. Dioicous. Perichaetia both terminal and lateral in the same species and occasionally on the same plant (acrocarpous and pleurocarpous), often in clusters, inner leaves ovate, rounded or short-acuminate to apiculate, to 2.5 mm in length, strongly sheathing seta, lower cells rhombic, thick-walled throughout. Perigonia terminal and lateral in clusters. Seta ca. 1.5–2.3 cm in length, 1 per perichaetium, yellow, twisted clockwise; theca 1.6–2.1 mm in length, yellowish brown, elliptical, exothecial cells short-rectangular, 20–25 µm in width, thin-walled, stomates phaneropore, at base of theca, annulus of ca. 3 rows of smaller, vesiculose cells; peristome teeth 16, variously cleft (usually to base) or occasionally perforate, subulate, transparent, smooth or very weakly spirally striate, 110–180 µm in length, with ca. 6 articulations, straight, basal membrane absent. Operculum conic, ca. 0.7–0.8 mm in length, cells straight. Calyptra cucullate, smooth, ca. 2.6–2.8 mm in length. Spores ca. 10–13 µm in diameter, light brown, papillose. Laminal KOH color reaction orange to yellowish orange.

A small genus found on soil or rock generally in or near dry, Mediterranean climates; Europe (Spain), South Africa, western North America (California), southern South America, Australia, Tasmania and New Zealand.

Triquetrella papillata (Pl. 28, f. 1–11, NY!) has perichaetia that in some plants are terminal and in others are distinctly lateral on the stem, often clustered below a terminal perichaetium (cf. Ganguleea). Perigonia, too, are clustered both terminally and laterally near the stem apex on separate, entirely perigoniate plants. The “acropleurocarpous” condition may be an anomaly, but whether this also occurs elsewhere in the genus cannot be immediately determined since perichaetia-bearing herbarium specimens are uncommon. Catcheside (1980) indicated that sporophytes are rare in South Australia, and Brotherus (1924–25) found the genus mostly sterile.

Triquetrella is similar to Leptodontium in the 16 smooth or nearly smooth peristome teeth, mostly cleft to the base (Pl. 28, f. 11; 29, f. 7); strongly differentiated perichaetial leaves (Pl. 28, f. 10); stem usually without a central strand (Pl. 28, f. 3); squarrose, strongly reflexed cauline leaves; and absence of a differentiated epidermal layer on the ventral surface of the costa (Pl. 28, f. 9). Triquetrella differs from Leptodontium by the occasional presence of a stem central strand (in T. californica, Pl. 28, f. 12–14, which also lacks the otherwise characteristic triangular section of the stem); the short, triangular cauline leaves forming three distinct rows (Pl. 28, f. 1–2); and sharp, spiculose upper laminal papillae (blunt and columnar in sect. Leptodontium). An intermediate taxon is Leptodontium paradoxicum, which shares with Triquetrella two characters rare in Leptodontium: entire leaves and dorsal costal epidermis differentiated. On the other hand, Eddy (1990) said about Triquetrella that “the sum of its gametophytic and sporophytic characters strongly suggests that the genus is misplaced in the Pottiaceae,” without further explanation.

There are differences between the species of Triquetrella in length of the theca, leaf shape, acumination of the leaf apex, length of the decurrencies, and in presence or absence of the stem central strand, that might be used to distinguish taxa, but, in general, the species are much alike. Casas et al. (1993) summarized the differences between most of the species in their study of T. arapilensis. Triquetrella preissiana of Australia has been synonymized with T. papillata by Watts and Whitelegge (1902) according to Stone and Scott (1976); the type of the former name (BM!) is indeed taxonomically T. papillata.

Additional literature: Cour (1955), Moore et al. (1982), Müller (1897b), Stark (1980), Zander (1980a).

Number of accepted species: 9.

Species examined: T. arapilensis (FH), T. californica (FH, NY), T. filicaulis (NY), T. papillata (BM, DUKE, FH, NY), T. patagonica (FH), T. tristicha (NY).