Acromastigum cunninghamii (Steph.) A.Evans
Bazzania cunninghamii Steph., Hedwigia 32: 205. 1893.
Mastigobryum cunninghamii (Steph.) Steph., Sp. Hepat. 3: 540. 1909.
Plants loosely prostrate or erect and cushion-forming, typically bright pale yellowish green, rarely pure green or bluish green, distinctly nitid when dry; shoots small, to 1 mm wide. Branching pseudo-dichotomously furcate, the branches of Frullania type, widely spreading; branch half-leaf ± symmetric, narrowly ovate, undivided, subvittate, tapering to a sharp apex; first branch underleaf 2–3-lobed, similar in form to other underleaves, inserted on ventral or ventral-lateral side of branch, quite removed from branch base. Acromastigum -type branches common, stoloniform. Stem cortical cells distinctly differentiated, in 7 rows, moderately thick-walled (the outer tangential wall thicker), distinctly larger than the thin-walled medullary cells; cortical cells in dorsal view of surface very large (100–130 µm long), hexagonal, the ventral cortical cells ± quadrate, about half as large and at times broader than long. Leaves typically persistent, rarely caducous, horizontal, loosely imbricate, allowing little of stem exposed in dorsal aspect, obliquely spreading, the dorsal portion plane, the ventral ± convex, the apex somewhat deflexed (particularly the ventral lobe); leaves indistinctly vittate, asymmetrically narrowly ovate, 220–330 µm wide × 480–770 µm long, the insertion strongly incubous; apex ± equally bilobed to 0.3–0.4, the ventral lobe slightly longer or about equal in length to the dorsal but distinctly narrower, the lobes entire, terminating in a single cell or uniseriate row of 2 cells; dorsal lobe narrowly acute, 4–6 cells wide at base; ventral lobe linear, divergent to ± parallel with the dorsal (when flattened), biseriate for most of its length, 2(3) cells wide at the base; dorsal margin ± straight, cordate to subauriculate at base, extending to middle of stem or somewhat beyond, entire or somewhat sinuate; ventral margin nearly straight, entire. Cells of leaf evenly thick-walled, without distinct trigones, with 2 rows of larger, rectangular cells along the ventral margin of leaf and continuing into the ventral lobe, forming an indistinct vitta, the inner row often somewhat larger, the cells of vitta 20–30 µm wide × 24–37 µm long, the cells in the dorsal sector of leaf smaller, less regularly arranged, 19–29 µm wide and long; marginal cells of disc and lobes with outer walls thickened and forming a glistening border; surface smooth or the lobes ± distinctly papillose. Oil-bodies 1 per cell, colorless, homogeneous, the surface smooth, the oil-bodies spindle-shaped, 2 × 3–5 µm. Underleaves conspicuous, a little wider than the stem, erect and ± appressed to the stem, contiguous, moderately convex, orbicular to quadrate, 3-lobed to 0.35–0.65; lobes ligulate, 2–4 cells wide at base (the lobes subequal or the lateral lobes somewhat wider), the apex truncate to acute, entire, terminating in a single cell (or uniseriate row of 2 cells) or 2–4 laterally juxtaposed cells; disc margins ± straight to curved; cells of disc and lobes evenly thick-walled; disc margins entire; surface smooth or distinctly but finely papillose.
Androecia and gynoecia not seen.
Distribution and Ecology : Amphi-Pacific in distribution (Engel and Merrill, 1994): southern South America; New Zealand: Auckland Islands, Stewart Island (200 m), South Island (120–1200 m), North Island (60–1300 m). It is apparently sporadic but widespread in New Zealand and is known from Fiordland (Borland Burn, Lake McKerrow), Westland (Haast Pass), Western Nelson (Stockton Plateau, Mt. Glasgow), Gisborne (Urewera), Auckland (Herangi Ra., Kaimai Ra., Coromandel Peninsula) and Northland (Waipoua Forest) EPs.
Usually on rock, especially on the sides of boulders and on stones in periodically inundated streambeds, but also on rock walls exposed to water flow, and on humus in constantly damp places. On Stewart Island plants occurred in a protected pocket with Acromastigum marginatum 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). An Auckland Island specimen was on tree branches in the direct spray from a waterfall. In the South Island it may occur directly on rock substrate of a huge boulder as well as dripping cliff faces in Nothofagus menziesii forest (Haast Pass, 540 m and Blue Valley Track, 430–480 m) where it may form large, spongy pure masses. In the North Island known from Urewera Natl. Park (crest trail from Highway 38 toward Whakataka summit, growing loosely in a deep recess at a tree base in a Nothofagus fusca – N. menziesii forest, 930–1030 m) and the summit area of Te Rangaakapua (Huiarau Ra., Urewera Natl. Park, 1230–1320 m) on a vertical rock wall in a mossy forest dominated by N. menziesii with some Olearia colensoi. Also present on the Herangi Ra. (vicinity of plateau area S of Te Whakapatiki, ca. 720–750 m), beneath decaying leaves of Poa sp. at the base of a vertical cliff. It occurs in the Kaimai Ra. (Aongatete area, 60 m) where plants occurred on a vertical rock wall at the margin of a stream system near several pools and low waterfalls where periodic inundation occurs, and on Mt. Te Aroha (880–940 m) occurring over rock and forming pendent sheets in a forest dominated by N. menziesii. On Coromandel Peninsula (ridge between Webb Creek Track and Billy Goat Track, Coromandel Forest Park, 510–540 m) on a shaded moist bank at a creek edge in a scrub forest of Leptospermum scoparium, Weinmannia silvicola and Dacrydium cupressinum; also on Mt. Moehau (ca. 800–840 m) on vertical banks of an exposed rocky ridge below the summit area of “Little Moehau” in an area of rocky outcrops and shrub-heath communities including Coprosma foetidissima, Corokia buddleioides, Dracophyllum recurvum, Lepidothamnus laxifolius and Oreobolus pectinatus. On Mt. Glasgow (Westland, 1200 m) it was found in a water course in penalpine shrub-tussockland of Olearia colensoi, Chionochloa flavescens, C. pallens and C. australis.
Comments : The narrow, biseriate ventral lobes of the leaf (Fig. 88: 7), the firm texture of the plants and clear straw-yellow color will immediately distinguish Acromastigum cunninghamii from the other bilobed-leaved New Zealand species of the genus. The common A. colensoanum also lacks secondary pigments, but differs by its subequally lobed leaves, lax texture, grass-green color and thicker stems (the cortical cells often in more than 7 rows).
The leaves of Acromastigum cunninghamii have a distinctive type of vitta, which is not intramarginal, but consists of 2 regular rows of larger quadrate cells along the ventral margin which extend distally to form the biseriate ventral lobe (Fig. 88: 7). The cell walls of the leaf are often suffused by a pale yellow pigment and are evenly thickened, except for the outer walls of the cells along the leaf margin, which are thicker (Fig. 88: 7) and form a narrow, glistening border.
Populations of Acromastigum cunninghamii from southern Chile differ by having more sinuate leaf margins and a coarsely papillose surface, but are otherwise similar to the New Zealand plants.
