16. TETRACOSCINODON Plate 20.

Tetracoscinodon R. Br. ter, Trans. & Proc. New Zealand Inst. 29: 532, 1897. Type: Tetracoscinodon hectorii R. Br. ter.

Plants growing in clumps or turf, green above, tan below. Stems blackish brown, branching occasionally, 1–3 cm in length, transverse section rounded-pentagonal, central strand absent, cells of the central cylinder large, 30–45 µm in diam., sclerodermis present, of 1–2 layers of stereids, hyalodermis absent; axillary hairs ca. 10 cells in length, all hyaline or basal cell thicker walled; rhizoids sparse. Leaves when dry appressed-incurved, when moist rigid, weakly spreading from the insertion, long-triangular to linear, 2–3 mm in length, upper lamina broadly and deeply channeled across leaf, margins plane or seldom weakly recurved, entire (minutely crenulate by projecting cell walls and papillae); apex setaceous and very narrowly obtuse; base triangular, broadest at insertion; costa percurrent, superficial cells on both sides of costa variously papillose and quadrate or elongate and smooth, 4–6 rows of cells across costa ventrally at midleaf, costal transverse section semicircular, two stereid bands present, epidermis present on both sides of costa, guide cells 4–6 in 1 layer, hydroid strand absent; upper laminal cells quadrate to short-rectangular, 8–12 µm in width, 1–2:1, walls evenly thickened, superficially bulging on both sides; papillae bifid, crowded, 3–6 per lumen; differentiated basal cells filling the triangular leaf base, rectangular, little wider than upper cells, 3–5:1, walls evenly thickened, smooth, bulging more strongly dorsally than ventrally, somewhat longer on the margins. Dioicous. Perichaetia terminal, inner leaves lanceolate, little longer than the cauline, convolute-sheathing in lower half, lower cells long rhomboidal in sheathing portion. Perigonia terminal, not gemmate, inner leaves sheathing below, paraphyses linear. Seta ca. 1 cm in length, 1 per perichaetium, brown, twisted clockwise; theca 0.6–1.5 mm in length, dark brown, short-cylindrical, exothecial cells rectangular, thin-walled, stomates phaneropore, at base of theca, mouth of capsule rather thick-walled with a somewhat swollen circumstomal ring several layers of cells in thickness bearing above it 4–6 rows of dark brown, vesiculose annular cells; peristome teeth ca. 16, flat, short-triangular, strongly incurved, much perforated and often cleft into 2–4 rami, smooth, covered externally by a hyaline membrane, 150–200 µm in length, with ca. 6–10 articulations, straight, basal membrane absent or present but low, smooth. Operculum long-conic, usually inclined, 0.5–1.0 mm in length, cells straight. Calyptra cucullate, smooth, ca. 2 mm in length. Spores large, 25–35 µm in diameter, brown, papillose. Laminal KOH color reaction yellow.

This is an infrequent taxon restricted to New Zealand where it is found usually encrusted with limestone deposits on dripping rocks.

Dixon (1923) was correct in synonymizing Brown's Tetracoscinodon hectorii with Eucladium irroratum as evidenced by authentic material of both names at NY, but this species differs widely from Eucladium ((q.v.) in important features that require recognition of a separate genus. Tetracoscinodon shares many apparently significant characters with Leptobarbula and Barbula, such as the stem section showing rather large central cylinder cells and a strong sclerodermis (Pl. 20, f. 3), a long-triangular leaf shape (Pl. 20, f. 4–7), superficially bulging upper laminal cells with crowded bifid papillae (Pl. 20, f. 13), and yellow color in KOH. It shares with Tridontium (Grimmiaceae, Scoulerioideae) and Dialytrichia a hygric habitat and relatively pachydermous capsule. Like Tridontium (see Excluded Taxa), the peristome (Pl. 20, f. 15–16) of Tetracoscinodon has an adherent hyaline membrane, but in the former genus the teeth are closely spiculose. The peristome o f Tetracoscinodon, in being smooth, extremely thin periclinally, and in having transverse joints that often do not go all the way across the tooth but instead angle down to intersect the next upper or lower joint, has the appearance of derivation from the outer rather then the inner peristomial layer. This needs further study. The most salient characters of Tetracoscinodon are its black stems with large cells in the central cylinder and lacking a central strand; the rigid, long-triangular to linear leaves with narrowly obtuse apices and papillose, quadrate to short-rectangular superficial cells dorsally; the rather large and crowded bifid upper laminal papillae; the rather thick-walled basal cells (Pl. 20, f. 10); the circumstomal ring of the capsule; and the calcareous incrustation generally found on the lower parts of the plants.

Additional literature: Brotherus (1924–25), Sainsbury (1955).

Number of accepted species: 1.

Species examined: T. irroratus (NY).

New combination: Tetracoscinodon irroratus (Mitt. in Hook. f.) Zand., comb. nov. (Weissia irrorata Mitt. in Hook. f., Handb. New Zealand Fl. 404, 1867).