Plants, red-brown, small, main shoots to ca. 425 µm wide [marginal dorsal lobe cilia excluded] (from Schuster, 1970, 340–370 µm wide). Leading stem to 50µm in diam. (Schuster 1970: 35–42µm), 5–6 cells wide, 10–15 cortical cells and 7–10 medullary cells, both with firm, thick, walls, and irregularly-shaped lumen; cortical cells slightly smaller than medullary cells, and the walls of the former often slightly thicker and deeper pigmented than those of the medullary cells. Branching often regularly pinnate, occasionally bipinnate. Dimorphic branching with both Frullania-type (FB) and Lejeunea-type branching. Initial branching appendages associated with FB: Rostrata-type i.e. first branch underleaf (BUL1) always with three distinct segments, the ventral lamina divided for ½ its length into two subequally sized lobes+ 1 dorsal saccate lobe, and the first branch leaf (BL1) ± characteristic of normal stem leaves (i.e.BL1: 1 explanate dorsal lobe + 1 saccate lobule + 1 stylus); or Apiculata-type i.e. both BUL1 and BL1 with 3 explanate to at most sulcate appendages (saccate appendages absent) with leaves characteristic of the main stem developing at BL2–BL3 (BL4). Initial appendages of LB: BUL1 and BL1–3 are always reduced in size and lobule-free, formation of normal saccate leaves occurring thereafter at BL2–BL4. Stemleavesof main branch contiguous (Hattori et al. 1972: to ± remote or slightly imbricate),± flat when dry and wet (Hattori et al. 1972: to slightly squarrose), dorsal lobes broadly ovate to asymmetrically elliptical and acute at the apex (Schuster 1970: apiculate or acuminate-spinose); to 220 µm long × 140 µm wide, dorsal base not beyond farther edge of stem; margin with (1) 2–3 (4) rows of ±colourless cells, cells of the outermost layer radially elongated and united in pairs forming jagged, irregular, spinose teeth, the resulting teeth to ca. 30 µm long × 15 µm wide; dorsal lobe typically with long-acuminate to apiculate apices (2–3 cells near base and extending to 3–5 cells in length and ca. 50 µm long), occasionally lobes tapering to triangular, acute, apices; non-auriculate at the base, and with a smooth dorsal cell surface. Lobules ± remote from the stem, lobule attached to main stem by a stalk of 2 (3) cells, stalk containing a single conspicuous, elongated, heavily thick-walled cell, to 30 µm long; lobuli at angles of 35–55º with the stem so that lobules tilted outwards (Schuster 1970: 15–45º); lobules slightly darker or similar in colour to other organs; uniformly inflated, but conspicuously dorsiventrally compressed near mouthas compared to gibbous upper half, smooth, obovoid, and ca. 1.5–2× long as wide, to 110µm long × 50 µm wide (Schuster 1970: 130–150 × 75–80 µm; Hattori et al. 1972: ca. 170 × 80 µm), ca. to 10–12 cells in length; lobuli ± large in proportion to the leaf-lobe (lobule area obscuring 0.35–0.5× the exposed area of the dorsal lobe), the opening extending along the abaxial lobule margin; immediately above the slit of the lobule mouth there are usually 2 enlarged, heavily thick-walled, elongated cells (cell cavity 1.5–2× long as wide); the free lobular mouth arched, with 1 layer of hyaline, thin-walled, radially elongated cells, such that the lobule mouth appears fan-like, lobule apex obtuse. Stylus, distinct, ± large, equal to subequal in size to stem underleaf, subtriangular to triangular, up to 50 µm long, (2) 3–4 cells wide at base, 5–12 cells in total, occasionally with a slime papilla at the apex. Underleaves of leading stems, small in size (ca. 0.1) the size of leaf lobes); distant from each other; usually slightly longer than wide, ovate to oblong in outline, to 55 µm long × 30 µm wide, (Hattori et al. 1972: to 70 µm long × 40 µm wide), 0.8–1.0× as wide as the stem, broadest at middle, to 4 (6) cells wide; lateral margins entire; apex of underleaf bilobed to 0.4–0.5 its length, lobes separated by a very narrow V-shaped sinus, lobes 2 (3) cells wide at base and only 4–5 (6) cells long, with acute to subacute apices. Rhizoid-initial area not seen. Secondary branching similar in size to the main stem.
Cells of stem leaf-lobes distinctly dimorphic: (1) Lobe marginal cells hyaline and thin-walled, in 2-3 rows [Hattori et al. 1972: (1) 2–3 (4)], the outermost layer as described above forming spinose teeth, the inner layers rectangular (to 20 µm long × 15 wide) to quadrate (to 15 µm × 15 µm) [Hattori et al. 1972: ca. 20–25 µm × 15]; (2) remaining cells, including median cells, with distinct heavily thickened and pigmented (± yellow-brown) walls, intermediate thickening ± absent, appearing ± subquadrate to rectangular, with many cells also distinctly 6–7 -sided, 12–18 µm long × 10.5–12 µm wide; cells becoming gradually larger towards the base, increasing in wall thickness, trigones remaining ± indistinct, cell cavities to 33 µm long × 15 µm wide [Hattori et al.: 1972 ‘toward the base cells ca. 10–20 µm × 7–10 µm; walls of basal cells increasing in thickness, and with rare to occasional, indistinct, intermediate thickenings. Cells of the styli and underleaf similar to those of the median leaf-lobe cells. Median cells oflobuleca. 1.5–2.5× longer than wide, cell cavities to 16 µm long × 9 µm wide, walls flexuose throughout the lobule, with indistinct trigones, but with distinct, small, nodulose intermediate thickenings (becoming increasingly flexuose towards the lobule mouth). Oil-bodies: no records. Asexual reproduction;none known.
No fertile material was available for study. Schuster (1972) describes the following: Autoicous? Androecia suborbicular in outline, button-shaped, of usually 2 (3) pairs of tightly imbricate bracts, at apices of long or short branches. Gynoecia with one subfloral innovation. Bracts in a single cycle, to 350 µm long, the lobe oblong-elliptical, similarly margined as leaves; lobules ca. 0.7–0.85 length of lobe, large, also margined. Bracteole obovate-spatulate, emarginated to shallowly bilobed, lobes broad, apiculate, sinus shallow, semi lunar; margins dentate and hyaline as on leaves. Hattori et al. (1972) citing Pearson, 1922, described the perianth as pyriform, obovate, 3-keeled (ventral keel wide and obtuse), keels all smooth, flat dorsally. However, this may be erroneous because Schuster (1970) had already highlighted that Pearson’s diagnosis was based on two or three species.
Affinities, differentiation & variation: Some features remain inadequately described and require further investigation, especially features associated with the perianth and sporophyte for which there is no data. However, despite this it remains a very distinctive species within Frullania and along with the other three members of the section are the only species with toothed leaf-lobe margins.
Geographic distribution: Only known from New Caledonia where it would appear to be quite common. Precise localities are provided by Hattori et al. (1972) and Hattori (1984a, 1986a). This species was recorded for New Zealand in error by Hattori et al. (1972), but later corrected by Hattori (1986a).
The above lengthy description, partially derived from Schuster (1970), is deemed necessary because certain criteria, which Schuster regarded as generic (or subgeneric) have proved to be species characters. The present description brings out more fully the species criteria; the most important are in italics that separate this species from other species in sect. Microfrullania. Schuster (1970) stated that Herzog, 1953, illustrated F. microscopica and, effectively, selected the sharply toothed plant as the lectotype; Schuster also noted that Pearson’s drawings were to a large extent based on the plants segregated as F. neocaledonica. Frullania microscopica (as Schusterella microscopica) was selected by Hattori et al. (1972) as the type species of Schusterella.
Schuster (1970) stated that the shallowly bilobed bracteole is a diagnostic feature of this species; however, shallowly bilobed bracteoles may also be found in some forms of F. truncata. Schuster ibid also concluded that the initial branching appendages and branching patterns (e.g., Lejeunea-type branching) preclude leaving Frullania microscopica and its allies in Frullania. However, Lejeunea-type branching has been found in other species of subg. Microfrullania as well as in species from the subgenera Diastaloba, Frullania and Australes.
von Konrat, M. J., Braggins, J. E., Asakawa, Y. & Toyota, M. 2006. Frullania chevalieri (Jubulaceae) in New Zealand, with a reassessment of Schusterella. The Bryologist 109(2): 141-156.