Acromastigum marginatum E.A.Hodgs.
Acromastigum marginatum E.A.Hodgs., Trans. Roy. Soc. New Zealand 82: 22. pl. 2, f. 10, 11. 1954.
Holotype: New Zealand, Great Barrier Is., Forestry Camp, 800 ft., 10 April 1952, Lloyd 39 (MPN hb. Hodgson no. 8433, non vidi); isotype: (CHR!).
Plants rigid and wire-like, fragile, loosely creeping among other cryptogams, bright green when fresh, pale translucent yellow-green in herb., without secondary pigments, dull when dry; shoots small, 665–770 µm wide. Branching ± regularly pseudo-dichotomously furcate, the branches of Frullania type, widely spreading; branch half-leaf slightly asymmetrically ovate, undivided, nonvittate, tapering to a sharp apex, cordate at base; first branch underleaf 2-lobed, inserted on ventral-lateral side of juncture of main axis and branch, free and often distant from underleaf of main axis. Acromastigum -type branches common, stoloniform, rarely reverting to leafy. Stem cortical cells distinctly differentiated, in cross section in 7 rows, moderately thin-walled except for the strongly thickened outer wall (the ventral 2 rows much smaller), distinctly larger than the thin-walled medullary cells which are in 7–8 rows; cortical cells in dorsal view of surface very large, 46–53 µm wide × 84–96 µm long, ± hexagonal, the ventral cortical cells ± quadrate, 26–32 µm wide × 34–43 µm long. Leaves rigid, fragile, easily tearing, loosely imbricate, with little of stem exposed in dorsal aspect, widely spreading, plane to slightly convex, with a thickened, pellucid margin, subvittate, asymmetrically narrowly ovate, 210–240 µm wide × 315–355 µm long, the insertion moderately incubous; leaves shallowly and strongly asymmetrically bilobed to ca. 0.15–0.2, the ventral lobe much larger than the dorsal, the lobes entire, terminating in a single cell or 2 superposed cells, the dorsal lobe truncate or reduced to a tooth or crenulation, the ventral lobe acute, 4–5(6) cells wide at base; dorsal margin broadly and gently curved, cordate to subauriculate at base, extending to middle of stem or somewhat beyond, entire or somewhat sinuate, not decurrent; ventral margin straight or slightly curved distally, abruptly curved near the base, entire, not decurrent. Cells of leaf evenly very thick-walled, with a subvitta in the median-basal area somewhat nearer the ventral margin than the dorsal, separated from the ventral margin by 2–3 rows of cells; cells ± in longitudinal rows, those outside the vitta in median sector of leaf 12–14 µm wide and long (the vitta cells larger, 18–24 µm wide × 22–25 µm long); surface striate-papillose along the margins of leaves, the dorsal surface coarsely papillose, the ventral almost smooth, except at margins. Underleaves large, to 2× stem width, contiguous, oblate in outline, 3-lobed to ca. 0.5; lobes subattenuate, 4–7(11) cells wide at base (the lobes subequal or the lateral lobes somewhat wider), the apex obtuse to acute, entire, terminating in a single cell or more commonly 2–4 laterally juxtaposed cells; disc margins broadly and distinctly curved, dilated near base into a rounded or angular projection, then often auriculate; cells of disc and lobes evenly thick-walled; surface papillose.
Androecia and gynoecia not seen.
Distribution and Ecology : Endemic to New Zealand, where it has a broad but evidently sporadic distribution; present on Stewart Island (20–200 m), South Island (20–700 m), North Island (ca. 350 m). Known from Rakiura (Port Pegasus, Tin Ra.), Fiordland (Secretary Island, Lake Manapouri), Westland (Cascade Plateau, Mt. Te Kinga), Western Nelson (Denniston Plateau, Stockton Plateau, Marino Mtns., Pakawau), Volcanic Plateau (Kaimai Ra.), Auckland (Coromandel, Great Barrier Island) and Northland (Waipoua) EPs.
Usually under forest (including Agathis australis – Beilschmiedia forest, Nothofagus menziesii forest, Dacrydium cupressinum – Weinmannia racemosa forest) or low podocarp forest or scrub (Lepidothamnus intermedius or Halocarpus bidwillii scrub with Leptospermum scoparium). It is found on tree bases, rarely on tree trunks, on vertical or slightly overhanging rock walls protected from direct rainfall, and on forest floor humus. Associated species are Acromastigum anisostomum, Bazzania monilinervis, B. nitida, Porina exocha, Hymenophyllum armstrongii, H. demissum, H. flabellatum, Kurzia hippuroides, Metrosideros diffusa, Paraschistochila conchophylla, Psiloclada clandestina, Ptychomnion aciculare, Riccardia crassa and Zoopsis argentea.
On Stewart Island plants occurred with Acromastigum cunninghamii over soil deep in a protected pocket at the base of a large rocky outcrop in a podocarp–hardwood forest including Dacrydium cupressinum and Weinmannia racemosa (Port Pegasus, vicinity of Tin Ra. Track, 200 m). In the South Island known from 200 m on Secretary Island, Fiordland, and at 135 m in the Cascade ultramafic moraine (W of Martyr Saddle, SSW of Jackson Bay), an area of ultramafic rocks and outcrops with rather open vegetation consisting of mainly of Gleichenia, Lycopodium, Juncus, the lichen Cladonia and scattered Leptospermum scoparium. In the North Island on the Kaimai Ra. (Aongatete area, 60 m) where plants occurred on a vertical rock wall above a stream system near several pools and low waterfalls. Also known from the summit of Table Mtn. (Coromandel Forest Park, 835 m), on the side of a bryophyte-covered log as well as over bark at tree base in a wet mossy forest of Lepidothamnus intermedius, Ixerba brexioides and Dacrydium cupressinum with occasional Phyllocladus glaucus. In Waipoua Forest (track to Te Matua Ngahere, ca. 340 m) at the base of a huge Agathis tree in mixed Agathis australis – Dacrydium cupressinum forest with other podocarps and with a dense ground tier of Gahnia xanthocarpa. In more humid sites in Waipoua Forest found loosely in masses of vegetation of a vertical stream bank in a steep-sided stream valley (Waikohatu Stream, 290 m). In Omahuta Forest Kauri Sanctuary (E of Mangamuka Bridge, Northland, 260 m) on bryophyte-covered banks in Agathis australis forest with occasional broadleaf and podocarp species. The type occurred with Hymenophyllum armstrongii and Bazzania novae-zelandiae at the base of a Knightia excelsa trunk at 245 m on Great Barrier Island.
Comments : A distinctive plant not to be confused with any of our other species. The plants are small, at most 770 µm wide and lack secondary pigments. No New Zealand Acromastigum has the combination of the reduced dorsal lobe, often being only a low, rounded or truncate projection (Fig. 89: 1), the exceedingly thick-walled cells that are larger in the median-basal sector of the leaf and form a subvitta of 2–3 rows (Fig. 89: 1) and the coarsely papillose surface present at least throughout the median and distal cells (Fig. 89: 4).
