23. Triquetrella Müller Hal., Oesterr. Bot. Z. 47: 421. 1897.
[Latin triquetrus, three edged, and -ella, diminutive, alluding to leaves commonly arranged in three rows]
Richard H. Zander
Plants forming mats, yellowish or blackish green distally, brown or blackish proximally. Stems to 7 cm; hyalodermis absent, sclerodermis present, of 1-3 layers of stereid cells, central strand present [absent]; axillary hairs to 9 cells in length, the proximal 1-2 cells thick-walled. Leaves appressed- to spreading-incurved when dry, widely spreading to squarrose, strongly reflexed when moist; triangular to ovate-triangular, adaxial surface keeled, narrowly channeled along costa, ca. 2 mm; base ovate, proximal margins long- and broadly decurrent; distal margins recurved in middle 3/4-4/5 of leaf, entire to weakly serrulate near apex; apex narrowly acute to shortly acuminate; costa percurrent, adaxial outgrowths absent, adaxial cells elongate, in 2(-4) rows; transverse section ovate to semicircular, adaxial epidermis absent, adaxial stereid band present or absent, guide cells 2-4 in 1 layer, hydroid strand absent, abaxial stereid band present, crescentic to circular in sectional shape, abaxial epidermis weakly differentiated; proximal cells weakly differentiated in a very small group medially, occasionally across insertion, rectangular, little wider than distal cells, 2-4:1, proximal cells thick-walled, somewhat porose; distal medial cells rounded rhombic to quadrate, ca. 9-11 µm wide, 1:1, 1-stratose; papillae spiculose, mostly simple to 2-fid, 1 per lumen, cell walls thickened, weakly trigonous, weakly convex to distinctly bulging on both sides. Specialized asexual reproduction not seen. [Sexual condition dioicous. Perichaetia terminal and lateral, interior leaves strongly sheathing, ovate, rounded or shortly acuminate to apiculate. Seta elongate. Capsule stegocarpous, theca elliptic, annulus of ca. 3 rows of smaller, vesiculose cells; operculum conic; peristome teeth 16, variously cleft (usually to base) or perforate, subulate, transparent, straight. Calyptra cucullate. Spores ca. 10-13 µm.] KOH laminal color reaction orange to yellowish orange.
Species 9 (1 in the flora): w North America, s South America, s Africa, Pacific Islands (New Zealand), Australia.
Triquetrella is distinctive in the stems rounded-triangular in section though this character is varies to rounded-pentagonal in the one species in the flora area. Although not fruiting in that area(and rarely so elsewhere in the world), the genus is unique in having both acrocarpous and pleurocarpous perichaetia on the same plant (R. H. Zander 1993). Unlike the similar Leptodontium, Triquetrella may occasionally show a small central strand (except, again, in the flora area).
Stark, L. R. 1980. Triquetrella in North America. Bryologist 83: 363-364. Zander, R. H. 1980. Acid-base color reactions: The status of Triquetrella ferruginea, Barbula inaequalifolia and B. calcarea. Bryologist 83: 228-233.