Gymnomitrion cuspidatum (Berggr.) R.M.Schust.
Cesia cuspidata Berggr., On New Zealand Hepat. 1. f. 1. 1898.
Acolea cuspidata (Berggr.) Steph., Sp. Hepat. 2: 7. 1901.
Gymnomitrion cuspidatum (Berggr.) R.M.Schust., J. Hattori Bot. Lab. 26: 280. 1963.
Type: New Zealand, South Is., Porter’s Pass, Mt. Torlesse, 1200 m, Feb. 1874, Berggren; South Is., Bealey River, Otira Gorge, Feb. 1874, Berggren.
Plants rather fleshy, soft-textured when moist, prostrate but with shoot apices ± ascending, whitish green to whitish, appearing bleached, the shoots densely leafy, somewhat complanate, flattened dorsally, strongly convex ventrally (due to the markedly dorsally assurgent, closely imbricate leaves), the shoots to 1.3 mm wide. Branching sparing to common, the branches all lateral-intercalary; microphyllous geotropic axes rare to sparingly developed. Leaves largely hyaline, vertically oriented, notably dorsally assurgent, mostly obliquely laterally spreading, ranging to suberect, densely imbricate, the stem hidden or virtually so, loosely complanate, the dorsal margins of the leaves erect to narrowly reflexed, the dorsal bases extended across the stem, collectively defining an obscure to distinct longitudinal groove on the dorsal face of the shoot; leaves ovate to elliptic-ovate to elliptic-rectangular, often a little asymmetrical, with one side somewhat more arched than the other, 220–315 µm wide × 399–480 µm long to 450–485 µm wide × 650–715 µm long, bifid to (0.25)0.3–0.45(0.5), the sinus acute; lobes ± parallel, or, more often, feebly divergent (then distal half of leaf almost parallel-sided), their tips usually somewhat divergent, the lobes acute, sharp, cuspidate, long drawn out, terminating in 1–2 elongated (or 2–3 shorter) cells, the lobe margins plane and not recurved, entire or only weakly crenulate by projecting walls of the marginal row of cells. Cells maximally incrassate, the walls very thick, hyaline (hence the whitish color, becoming bleached in appearance when dry), the middle lamella perceptible; cells everywhere guttulate, in lobe apices very strongly thick-walled both on their surfaces (hence cell outlines often rather obscure) and between cells, the lumina mostly ellipsoidal to lozenge-shaped, sometimes linear on lobe margins, quite variable in size and shape; cells in lobe apices and margins often narrow and oriented parallel to margin or obliquely to margin, small, 12–17 × 13–20 µm, the lumina reduced; cells of lobes within margins mostly longitudinally oriented and with ellipsoidal lumina; cells of median portion of lamina somewhat less thick-walled than in lobes, 14–19 × 19–30 µm to 15–18 × (26)30–36(40) µm; surface often distinctly asperulate (at times barely perceptibly so). Underleaves lacking.
Autoecious. Androecia terminal but becoming intercalary on long axes; bracts leaf-like, but with bases shallowly ventricose and lobe margins sporadically crenulate-denticulate; antheridia 1 per bract (always?). Gynoecia usually on lateral-intercalary branches of variable length, sometimes quite abbreviated and not developing mature leaves prior to bract development; bracts grading gradually into leaves, closely imbricate, typically two-ranked in such a manner as to leave a perceptible dorsal groove; innermost bracts narrowly oblong, bifid to 0.4–0.45, the lobes narrowly acute, sporadically with 1–few sharp, 1(2)-celled teeth, the flanks often with a coarse tooth below the lobe bases; within the pair of largest bracts are 2(3) multiform, somewhat abbreviated, pleated and variably 3–4(5)-lobed structures (?derived by reduction from the perianth), the lobes irregular, tapered, acuminate to caudate, mostly bearing a few sharp, remote, 1–2-celled, often arched, spinose teeth; innermost reduced bractlets (always?) absent. Perianth wholly lacking.
Seta short, elevating capsule not far beyond level of bracts. Capsule spherical, the wall 2-stratose, the wall 18–19 µm thick, the outer layer of cells 3× the thickness of inner layer, the outer layer of cells with two-phase development, the longitudinal walls bearing low, rounded, occasionally ± coalescent nodular thickenings lending a distinctly sinuous appearance alternating with walls devoid of thickenings or with isolated smaller nodular thickenings, the transverse walls lacking thickenings or sporadically with a solitary low thickening; inner layer of cells with longitudinal walls bearing well-developed, low, rounded, often coalescent nodular thickenings lending a distinctly sinuous appearance, the pattern rather similar to the outer wall but the thickenings not as strongly developed, the transverse walls often with nodular thickenings but these smaller than those of the vertical walls.
Spores red-brown, 13.9–14.9 µm in diam. distinctly areolate, the ridges rather thick. Elaters not seen.
Distribution and Ecology : Endemic to New Zealand: South Island ([520]1000–1480 m), North Island (1350–1660 m). Known from Fiordland (Mt. Burns, Lake Monk), Westland, Otago (Rock and Pillar Ra.), Canterbury, Western Nelson (Lookout Ra.) and Volcanic Plateau EPs.
Rather common in the penalpine and alpine zones over rock or in pockets between boulders or outcrops, particularly where soil has accumulated. Also on flat rock of cliff faces. The species is able to tolerate considerable exposure, e.g., occurring over bare soil of an exposed ridge at 1250–1450 m in alpine vegetation (below and W of Mt. Armstrong, Mt. Aspiring Natl. Park). It exceptionally occurs in forests, e.g., over a shaded cliff face in a Nothofagus menziesii forest at 760–800 m (Governors Bush, Mt. Cook Natl. Park) and on the roof of a rock overhang in a N. menziesii forest at Haast Pass (540 m) with Lepidozia pumila. Plants often occur as isolated stems or they may be gregarious and form thin mats. It is associated with Andreaea mutabilis, Arthroraphis alpina, Bartramia papillata, Cryptochila grandiflora, Dicranoweisia antarctica, Diplophyllum domesticum, Ditrichum brevirostre, Grimmia incrassicapsulis and Racomitrium crispulum.
Comments : This species and Gymnomitrion strictum are quite variable and need to be carefully compared utilizing large suites of specimens. Sinus depth, the degree of surface roughening (both species are variously asperulate) and pigmentation all are to some degree variable. In general, however, plants of G. cuspidatum are whitish green, with pigmentation only sparsely developed, have leaves more deeply lobed with leaf lobes distinctly asperulate. Plants of G. strictum, on the other hand, are nearly always pigmented, have leaves more shallowly lobed, with leaf lobes weakly and often indistinctly asperulate. Schuster (2002a, p. 569) remarks that plants of G. cuspidatum are “virtually devoid of brownish pigments; in the field there is a distinct whitish green or whitish aspect to the plants.”
Sinus depth should be measured with care, since leaves, when flattened, often tear at the sinus base. Prior to measurements the sinus should be examined under higher magnification to determine the extent of the tear; uneven cell walls often will indicate tear presence and the asperulate surface will indicate absence.
The two New Zealand species are unique in the genus in having distinctly areolate spores.
