Acromastigum cavifolium R.M.Schust.
Acromastigum cavifolium R.M.Schust., J. Hattori Bot. Lab. 26: 257. 1963.
Type: New Zealand, Stewart Is., Tin Ra., Schuster 53119.
Plants appearing radially symmetric, rigid and appearing stout and fleshy, rather fragile, loosely prostrate, translucent, pure light green in life, pale straw-yellow in herb., distinctly nitid when dry; shoots small, to 1 mm wide. Branching of Frullania type, widely spreading; branch half-leaf similar to leaves but somewhat narrower at apex, symmetric, ovate, undivided, tapering to a narrow apex; first branch underleaf undivided, lingulate, faintly sulcate, inserted on ventral side of main axis well below branch and closely juxtaposed on one side to a leaf, but not connate with it, or inserted on the ventral side of branch just above the juncture of branch and main shoot. Acromastigum -type branches common, stoloniform, the half-underleaf resembling the first branch underleaf of Frullania -type branches. Ventral-intercalary branches rare, leafy. Stem with cortical cells moderately differentiated, in 14–16 rows, thick-walled (particularly the outer tangential wall), moderately larger than the distinctly thick-walled medullary cells. Leaves rigid, appearing thick and fleshy, vertical or nearly so, not or at most feebly elevated, squarrose at least in basal half, the distal sector becoming gently suberect; leaves distant to loosely imbricate, plane to slightly and broadly concave, not vittate, 320–475(640) µm wide × 430–640 µm long, transversely inserted and oriented, subsymmetrically narrowly ovate, with a glistening border formed by the strongly thickened free walls of the marginal cells; apex undivided, narrowly to broadly rounded to broadly obtuse (rarely retuse); dorsal and ventral margins similar although the dorsal at times ± ampliate, the margins straight distally, weakly cordate at the base, entire. Cells in ± regular longitudinal rows at least in median sector, highly uniform almost throughout the leaf, moderately thick-walled, trigones massive, coarse and nodular, at times confluent, commonly with leaf cell lumen bounded mostly by the massive trigones (except for the narrow, moderately thick-walled places between trigones); subapical cells 20–30 µm wide and long, the median cells remaining ± isodiametric, being 22–34 µm wide and long, the basal cells to 36 µm long; surface smooth, papillose at the margins. Oil-bodies (fide Schuster, 2000a) 1–2(3) per cell, finely granular-botryoidal, colorless to greyish, spherical and 4.5–5(6) µm in diam. to ovoid and 4.5–5.5 × 6–8 µm. Underleaves with orientation and shape ± similar to the leaves but smaller, somewhat broader than the stem, distant to weakly imbricate, slightly convex; apex undivided, rounded and entire or retuse or very shallowly and often asymmetrically bifid, with 3 slime papillae in the apical notch; margins entire; cells as in leaves; surface smooth.
Androecia hyaline, on short, determinate, tightly spicate, ventral-intercalary branches from main shoot, or from leading, leafy ventral-intercalary branches or (often) from stoloniform branches; bracts ventricose-cucullate, the apex with 2 small, closely approximate teeth; dorsal and ventral margins similar, entire and lacking slime papillae; antheridia 1 per bract, the stalk biseriate; bracteolar antheridia occasional, 2 per bract. Gynoecia on abbreviated ventral-intercalary branches issuing from main stem. Bracts of innermost series much larger than leaves but relatively small in proportion to perianth size, erect and closely appressed to perianth, the bracts concave-subcanaliculate, ovate, 4-lobulate, the median pair of lobes larger; lobes consisting of a few biseriate tiers from a base at most 4 cells wide, the lobe terminating in 2 laterally juxtaposed cells, a single cell or a uniseriate row of at most 2 cells, with each lobe terminating in a slime papilla; lamina in distal sector comprised of thick-walled cells with bulging trigones, the cells in basal portion thin-walled and with trigones minute or absent, the margins irregularly crenulate by the projecting, truncate, upper ends of some cells which each terminate in a slime papilla; bracteole similar in size and form. Perianth prominent, fusiform, terete below, trigonous above, plicate in distal ca. 0.25 and gradually narrowing to the contracted mouth, the mouth lobulate, the lobules each with 1- or 2-spinose, often contorted teeth composed of thick-walled cells, the teeth of a few laterally juxtaposed cells or, more often, comprised of a single cell or a uniseriate row of 2–3 cells.
Seta seen only in collapsed state. Capsule wall 32–36 µm thick, of 3 layers, the outer layer about equal to thickness of the other 2 layers or a little more; outer layer of cells short-rectangular, with two-phase development, the longitudinal walls with rather thick, nonsinuous, sheet-like thickenings and strong nodule-like thickenings alternating with walls that are devoid of thickenings, the transverse walls devoid of thickenings; innermost layer of cells narrowly long-rectangular, with semiannular bands, the bands usually complete.
Spores 15.4–19.7 µm in diam., deep red-brown, with rather distantly spaced, sharply defined papillae and short, wide vermiculate markings. Elaters not seen.
Distribution and Ecology : New Zealand: Stewart Island, South Island (0–1160 m), North Island (890 m); Australia: Tasmania. In New Zealand known from Fiordland (Henry Pass, Secretary Island), Westland (Jackson Bay, Paparoa Ra., ridge behind Westport, Stockton and Denniston plateaus) and Auckland (Mt. Moehau) EPs.
This species is infrequent and occurs scattered with other taxa or, less often, in ± pure but not dense mats. It may occur on stumps and peaty humus, or on tree bases, mixed with Acromastigum anisostomum, Adelanthus falcatus, Bazzania involuta, Cuspidatula monodon, Herbertus oldfieldianus, Heteroscyphus decipiens, Hymenophyllum armstrongii, Lepicolea scolopendra, Radula dentifolia, R. scariosa and Riccardia crassa, or bryophyte-covered tree bark (recorded on trunks of Lagarostrobos colensoi, Libocedrus bidwillii, Nothofagus menziesii, N. solandri var. cliffortioides and Phyllocladus alpinus) and then associated with Acrochila biserialis, Goebeliella cornigera, Heteroscyphus menziesii, Lepicolea scolopendra, Paraschistochila tuloides and Riccardia furtiva. The species is apparently confined to organic substrates in hyperhumid areas.
Comments : This is the species described by Hodgson (1954, p. 18) as Acromastigum integrifolium (Austin) A.Evans, a species which is now known to be restricted to the Hawaiian Islands. Schuster (1963a) listed several differences between A. cavifolium and A. integrifolium (as well as A. verticale of New Zealand), namely the strongly concave, spoon-shaped leaves (which are spreading but never squarrose) and the rounded leaf apices, which are only rarely retuse and never emarginate. The majority of the leaves are so concave that, when flattened under the cover glass, they tear. Distinctive is the very regular, almost unvarying leaf shape, with all leaves widest near the base and thus ovate-triangular in shape.
Of the New Zealand species of the genus, Acromastigum cavifolium can be confused only with A. verticale, but has basically symmetrically ovate leaves, often with blunt or narrowly truncate apices; it also has somewhat smaller cells, 20–30 µm wide and long in the subapical region.
