Acromastigum colensoanum (Mitt.) A.Evans
Mastigobryum colensoanum Mitt. in Hook.f., Bot. Antarc. Voy. 2: 147. pl. 100, f. 3. 1854. Bazzania colensoana (Mitt.) Carrington & Pearson, Pap. & Proc. Roy. Soc. Tasmania 1887: 50. 1888 (“colensoii”). Acromastigum colensoanum (Mitt.) A.Evans in Reimers, Hedwigia 73: 142. 1933.
Type: New Zealand, North Is., Tararua, Colenso.
Mastigobryum minutulum Colenso, Trans. & Proc. New Zealand Inst. 19: 288. 1887 (1886).
Type: New Zealand, Waipawa Co., near Norsewood, 1886, Colenso 1403 (BM!, G!).
Mastigobryum amoenum Colenso, Trans & Proc. New Zealand Inst. 19: 288. 1887 (1886).
Type: New Zealand, Waipawa Co., near Norsewood, 1886, Colenso.
Mastigobryum smaragdinum Colenso, Trans. & Proc. New Zealand Inst. 21: 67. 1889 (1888).
Type: New Zealand, Waipawa Co., S of Dannevirke, 1888, Colenso (BM!).
Mastigobryum erosifolium Steph. in Steph. & Watts, J. Proc. Roy. Soc. N. S. W. 48: 122. 1914.
Type: Australia, Cambewarra Mt., Oct. 1907, Watts 917 – c. per. (G!).
[Fig. 87; Fig. 90: 1, 2, oil-bodies, p. 410]
Plants delicate, soft and flexuous, grass-green to yellow-green, rarely bluish green, without secondary pigments, nitid when dry; shoots medium, to 1.8 mm wide. Branching pseudo-dichotomously furcate, the branches of Frullania type, widely spreading; branch half-leaf weakly asymmetric to ± symmetric, ovate, undivided, tapering to a narrowly rounded to sharply acute apex; first branch underleaf 2-lobed, inserted on ventral or ventral-lateral side of branch near the juncture of branch and main shoot. Acromastigum -type branches common, stoloniform. Ventral-intercalary branches sporadically produced, leafy. Stem fleshy in appearance, the cortical cells moderately differentiated, variable in number, somewhat larger than the medullary cells, in 14–16(18) rows, the radial walls thin like the medullary cells, the outer tangential walls somewhat thickened; cortical cells in dorsal view of surface short (ca. 50–70 µm long), the ventral cortical cells similar. Leaves typically persistent, exceptionally caducous, delicate, loosely imbricate, exposing much of stem in dorsal aspect, widely spreading, plane or slightly convex; leaves subvittate or not, asymmetrically narrowly ovate-rectangular, 360–530 µm wide × 730–900 µm long, the insertion strongly incubous, ± equally bilobed to 0.25–0.4, the ventral lobe often somewhat narrower and at times longer than the dorsal, the lobes acute, the dorsal often broadly so, the lobes at times apiculate, usually terminating in a single cell or sporadically in a uniseriate row of 2 cells, the dorsal lobe 7–12 cells wide at base, the ventral 5–7(8) cells wide; dorsal margin ± straight, cordate to subauriculate at base, extending to middle of stem or somewhat beyond, the ventral margin nearly straight, the margins of disc and lobes entire or somewhat sinuate. Cells of leaf thin-walled and with minute trigones or evenly thick-walled and with medium and straight-sided trigones, with a short indistinct vitta (apparent only on some leaves) consisting of several rows of somewhat larger, somewhat elongated cells (24–34 µm wide × 26–36 µm long) in the ventral sector of leaf near the base and separated from the margin by 1–3 rows of cells, the cells of the dorsal sector of the leaf smaller, less regularly arranged, 14–23 µm wide × 17–28 µm long; marginal cells of disc and lobes with outer walls somewhat thickened; surface smooth or finely but distinctly papillose, near the base striate-papillose. Oil-bodies restricted to basiscopic half of leaf and in all vitta cells, but some cells (especially those in basiscopic lobe) lacking them, the oil-bodies completely lacking in acroscopic half of leaf with no traces of droplets there, the oil-bodies in vitta very variable, (2)6–12 per cell, very pale grey, elliptic to linear, smooth but organized into large, irregular, subspherical masses of oil with segmentation lacking, or, if present, obscure and mostly appearing to be a surface feature, the oil-bodies appearing irregularly lumpy, 4–7 × 9–11.6 µm; oil-bodies in nonvittate cells along basiscopic margin, 2–6 per cell; oil-bodies in cells of leaf base smoother, less lumpy and more Bazzania -like in appearance. Chloroplasts packed in nonvittate cells. Underleaves small, often narrower than stem (particularly on larger diameter stems), appressed to the stem or slightly spreading, distant, quadrate to rectangular, 3-lobed to 0.6; lobes ligulate, 2–4 cells wide at base, the apex truncate (often retuse) to rounded to bluntly acute, entire, terminating in 2–4 laterally juxtaposed cells or, less commonly, in a single cell; disc margins ± straight to somewhat curved, with entire margins; cells of disc and lobes thin-walled, the outer tangential wall of marginal cells thickened; surface smooth.
Androecia on inconspicuous, short, determinate, tightly spicate, ventral-intercalary branches from leading shoots; bracts ventricose-cucullate, ± symmetrically bifid to ca. 0.3, the lobes broad acute, often apiculate, terminating in a uniseriate row of 2 cells; dorsal margin not perceptibly dilated, sparingly repand, at times crenulate, with a few slime papillae, otherwise entire; bracts monandrous; antheridial stalk biseriate; bracteolar antheridia absent. Gynoecia on abbreviated ventral-intercalary branches issuing from main stem, the gynoecium base slightly swollen and rhizoidous. Bracts of innermost series much larger than leaves, erect and closely ensheathing the perianth, the bracts concave-subcanaliculate, narrowly ovate, bilobed to ca. 0.3; lobes narrowly attenuate to linear, terminating in a uniseriate row of 2–3 cells, the lobe margins subentire or with a few remote crenulations; lamina composed of subrectangular, thin-walled cells, the marginal and submarginal cells ± rhomboidal, variable in shape, minutely and irregularly crenulate by projecting ends of cells, the margin on each side with an indistinct lobule in upper third; bracteole similar in size and form. Perianth prominent, straight, fusiform, terete below, the distal 0.75 pluriplicate and gradually narrowing to the contracted mouth, the mouth with 6 narrowly attenuate, somewhat sinuous lobes that each terminate in a uniseriate row of 2–3 cells, the lobe margins irregularly serrulate and at times with a few accessory teeth and laciniae; perianth 2-stratose in basal sector.
Seta with 8 rows of very large outer cells, the interior cells not seen. Capsule wall 42–45 µm thick, of 2 subequally thick layers; outer layer of cells subquadrate, with two-phase development, the longitudinal walls with rather thin, nonsinuous, sheet-like thickenings and several nodule-like to spine-like thickenings alternating with walls that are devoid of thickenings (or are sporadically locally thickened), the transverse walls devoid of thickenings or sporadically have an isolated nodule; innermost layer of cells ± tiered, mostly quadrate to occasionally short-rectangular, with semiannular bands 1–2 per cell, the bands frequently semicircular at the cell corners, rather wide, usually complete, rather frequently forked and anastomosing to delimit ill-defined, local fenestrae; tangentially oriented bands occasional (seen in capsule cross section).
Spores and elaters not seen.
Distribution and Ecology : New Zealand: Auckland Islands, Stewart Island (530 m), South Island (100–600 m), North Island (420–1100 m), Chatham Islands; Australia: Tasmania, New South Wales. Known from Fiordland, Otago, Westland, Sounds–Nelson, Southern North Island, Volcanic Plateau, Taranaki, Gisborne, Auckland and Northland EPs.
A relatively common species of wet forests. It occurs on bryophyte-covered logs, rotted stumps, tree buttresses (particularly in protected recesses between exposed roots at the tree base) and occasionally on tree-fern caudices. It also is found loosely creeping over soil deep in shaded, protected hollows or pockets, at times with Telaranea elegans and Saccogynidium australe, and it may form loose, soft mats on cliff faces. Also over soil on vertical mossy banks or mossy stream banks. In the Herangi Ra. (vicinity of plateau area S of Te Whakapatiki, ca. 720–750 m) over humus in a very narrow and shallow water channel in a small valley system, the vegetation consisting of Podocarpus hallii, Dracophyllum traversii and Weinmannia to 3–5 m tall. On Stewart Island it occurs deep in shaded, protected niches under tussock cover within mosaic communities of dense heath-forming shrubs to 3 m tall, penalpine herbs and dwarf heaths to 0.5 m tall, dominated by stunted Leptospermum scoparium and Dracophyllum and a ground tier including Empodisma minus (Mt. Rocky summit area, 530 m). Commonly accompanying species are Bazzania nitida, Leucobryum candidum, Rhizogonium distichum and Zoopsis argentea. Also found with Bazzania adnexa, Cuspidatula monodon, Psiloclada clandestina, Pyrrhobryum bifarium, Rhynchostegium tenuifolium, Saccogynidium australe, Trichocolea mollissima, Tylimanthus diversifolius, Wijkia extenuata, Zoopsis argentea and Z. setulosa. The habitats of this species seem to be more nutrient-rich and less constantly moist than those of other Acromastigum species, as indicated by some of the species that can be found with A. colensoanum.
Comments : This species is easy to recognize because of its grass-green color (secondary pigments totally absent) and the nonvittate, subsymmetrically lobed leaves, with the two lobes about equal in size and width (Fig. 87: 1, 2). The stems appear stout and fleshy, due to the stem cortex of more than 7 cell rows (Fig. 87: 8). This species is the only one in the genus here that is commonly seen with sporophytes.
The inner capsule wall occasionally has tangentially oriented bands; these are seen in capsule cross section and are oriented at right angles to the vertical bands that are so common in the Hepaticae. We know of no other instance of such tangential bands.
