Cephalomitrion R.M.Schust.
Cephalomitrion R.M.Schust., Nova Hedwigia 61: 350. 1995.
Type: Cephalomitrion aterrimum (Steph.) R.M.Schust. (≡Cephalozia aterrima Steph.)
Plants rigid, maximally wire-like, thread-like, pitch-black, the shoot tips and gynoecial regions often deep magenta, at times the stems pure green and the leaves claret-red, the plants small, 160–245 µm wide with leaves, but broader in ♂ and ♀ sectors, with shoots densely interwoven and, especially toward the base of the plant, entrapped with fine grains of sand. Branching common, irregular, the shoots often elongating and becoming arcuate, the branches all ventral-intercalary, at right angles to parent axis, apparently originating from near ventral angle of lateral leaves; geotropic stolons lacking. Stem filiform, the cortical cells in 1–2 layers, deep brown to blackish, rather firm-walled, larger than medullary cells; medullary cells very thick-walled, scarcely pigmented, the lumina rounded to guttulate. Rhizoids few or none, scattered and usually solitary. Leaves unistratose, so closely appressed to stem as to be almost invisible, remote below, contiguous to feebly imbricate toward shoot apices, scale-like, strongly concave, swollen just above insertion and forming a transverse ridge, the insertion transverse, extending to stem midline dorsally; leaves (when flattened) rounded-quadrate to suboblate-quadrate, (160)180–200(230) µm wide and long, larger in and near gynoecial sectors, bilobed to (0.25)0.35–0.5; lobes subacute to most often blunt at the tips, mostly 8–12 cells wide at base, the margins and sinus never reflexed, the margins vaguely crenulate by tumid cells, otherwise entire, the marginal cells not differentiated; sinus V-shaped, acute. Cells firm-walled above, thin in basal sector, lacking trigones, characteristically tumid, gibbous near margins (best seen in partial profile), irregular in shape and size, the median cells 9–11(13) × 12–15(18) µm, the lobe marginal and intramarginal cells 8–11(13) × 11–15 µm, the basal scarcely larger; surface smooth. Oil-bodies occupying a conspicuous portion of the cell, pale smokey grey, 4–8 per median disc cell, obscurely and indistinctly granular, with a hazy appearance, 3–4 µm and spherical to (2.8)3–3.5 × 5–6.5 µm, sporadically 5 × 6 µm. Chloroplasts large for cell size. Underleaves reduced to a spherical, papilliform cell, but near gynoecia sometimes narrow, comprised of 4–5 cells. Asexual reproduction absent.
Dioecious (the ♂ and ♀ plants usually intermingled), or, at least sometimes, autoecious. Androecia becoming intercalary, the bracts in 2–3(4) pairs, abruptly larger than adjacent sterile sectors, leaf-like but pouched in dorsal half of bract base; antheridia 1 per bract, the stalk uniseriate. Gynoecia terminating axes of various lengths, somewhat clavate-capitate, usually claret-red, not innovating; bracts polymorphic, in 2–3 series, those of innermost series closely sheathing perianth, concave, bilobed, the lobes triangular, the apices blunt to rounded, the lobe margins crenulate by tumid cells, otherwise entire; bracteole conspicuously connate with bracts on both sides, ovate, unlobed. Perianth ca. 0.45–0.55 emergent, slightly narrowed to the wide mouth, deeply 4(5)-plicate, the mouth often decolorate with age, obscurely crenulate with variable, only sporadically elongated cells; perianth 2-stratose at base, becoming unistratose below the middle.
Seta with 8 outer rows of cells and 4 rows of much smaller internal cells. Capsule ovoid to short-ellipsoidal, the walls 2-stratose; outer layer of cells variable but mostly rectangular, with one-phase ontogeny, the longitudinal walls all, with rare exceptions, and some or many transverse walls with well-defined nodular thickenings; inner layer of cells less regular, with delicate nodular thickenings on longer walls, often with weak semiannular bands.
Spores purplish brown to reddish brown, 9–10 µm in diam., almost smooth. Elaters weakly sinuous, 6–8 µm in diam., bispiral, the spirals rather broad, 2–2.2 µm wide.
A monotypic genus of Australasia. Description freely modified from Schuster (1995a).
References: Schuster (1972a, 1995a, 1996a, 2002a).
