Hygrolembidium acrocladum (Berggr.) R.M.Schust.
Aplozia lacerata Rodway, Tasman. Bryoph. 2: 32. 1916.
Type: Tasmania, Mt. Wellington plateau, ? Rodway (MANCH!).
Lembidium isodictyon Herzog, Ark. Bot. N.S. 1: 488. f. 6, 7. 1952 (1951).
[Fig. 113: 4, oil-bodies, p. 504; Figs. 116, 117]
Plants light green to light yellow-green, variable in size, the leafy shoots ranging from stoutly clavate, being only 650–750 µm wide and bearing 3–5 pairs of leaves to more robust, to 2.2 mm wide and bearing several to many pairs of leaves. Branching abundant, the leafy branches ventral- or lateral-intercalary and mostly from a system of creeping, freely branched, colorless, long slender stolons, the leafy branches rarely and sporadically issuing from leafy sectors of another leafy shoot and then only ventral-intercalary. Stem distinctly thick and fleshy for plant size, the cortex in 36–39 rows, leptodermous, poorly differentiated. Rhizoids mostly lacking on erect, leafy shoots, but if present, then from basal cells of underleaf or from stem at immediate base of underleaf. Leaves rather rigid, fleshy, polystratose in median and basal sectors, the median and distal sectors unistratose in an area below apex and within lateral margins; leaves in cross section toward base 3–5(6)-stratose in intramarginal sector, the marginal sector remaining polystratose or thinning to unistratose, the epidermal cells of leaf on average smaller in diameter than internal cells; leaves contiguous to closely imbricate, suberect to obliquely spreading, the insertion succubous in well-developed plants, ± transverse in smaller or weaker plants, the leaves deeply concave, at times subcupulate, orbicular (particularly in smaller plants) to suboblate, occasionally ovate, to 1120 µm wide × 1295 µm long when flattened; apex normally broadly rounded, less often truncate, sporadically repand, undivided, never retuse; lamina margins entire. Cells of apical sector subquadrate, at most short-rectangular, not elongate, the walls thin or slightly thickened, 22–36 µm wide × 22–45 µm long up to 35–40 µm wide × 35–50 µm long; median cells 24–32 µm wide × 32–56(62) µm long; basal cells 24–30 µm wide × 55–75 µm long; cells of unistratose region firm-walled, those of polystratose area leptodermous, delicate; surface smooth at least in median portion of leaf and often smooth throughout, distal cells occasionally faintly papillose, the marginal cells rarely so. Oil-bodies (in part after Schuster and Engel [1987b]) variable in number: 1–3 to 3–5, sometimes 6–9 per cell, coarsely and irregularly segmented and formed of a few variable, spherical segments; oil-bodies small, spherical and 4 µm in diam. to ovoid and 3–4.5 × 6–7(9) µm to 4–4.5 × 7–10 µm to broadly elliptic. Underleaves small, often inconspicuous and appearing as if lacking, the underleaves plane to weakly concave, wide-ovate to orbicular to suboblate, occasionally oblong or lingulate, the apex crenulate or with 1–3 teeth or irregular lobules; lamina margins entire or locally denticulate by projections of 1 or 2 cells.
Androecial branches originating from axils of underleaves, laxly spicate and at times subjulaceous; bracts erect, of similar form to leaves; antheridia 2–4 per bract, the stalk biseriate. Gynoecia on abbreviated ventral-intercalary branches, from lower, microphyllous sectors of leafy shoots; bracts and bracteoles concave, similar or bracteole somewhat narrower, the bracts considerably larger than leaves, ovate to wide-elliptic, the apex irregularly dentate or at times clearly 4-dentate-lobulate, the lamina margins with several teeth and (less often) ciliiform projections. Perianth very large for plant size, to 4.2 mm long × 1.4 mm in diam., subclavate to oblong-fusiform, cylindrical throughout or cylindrical below and faintly 3(4)-gonous above, the mouth crenulate to spinose dentate-lobulate; perianth 4–5-stratose at base.
Seta (fide Herzog, 1952) with 16–17 rows of outer cells. Capsule wall 4-stratose and 30–36 µm thick to 5-stratose and 42–46 µm thick; outer layer of cells equal to thickness of 1.8–3 of interior strata, the radial walls with nodular to spur-like thickenings on both longitudinal and most transverse walls, those of longitudinal walls sporadically extended tangentially to form complete, somewhat thickened semiannular bands; innermost layer of cells with radial walls often with ± continuous sheets of red-brown wall material, the radial walls also with rather thin semiannular bands and occasional nodular to spur-like thickenings.
Spores 15.8–17.8 µm in diam., the wall red-brown, with dense, low but sharply defined, close, papillose and short-vermiculate markings, 1.7–2.3× the elater diam. Elaters tortuous, bispiral, 7.2–9.6 µm in diam., the spirals 2.9–3.8 µm wide.
Distribution and Ecology : New Zealand: Stewart Island (600–690 m), South Island (560–1525 m), North Island (305–2000 m); Australia: Tasmania, Victoria, New South Wales. In New Zealand known from Fiordland (Hunter Mtns.), Otago (Pisa Ra., Old Man Ra., Maungatua, Swampy Summit, Lammermoor Ra., Rock and Pillar Ra.), Westland (Aspiring Natl. Park, Nelson Lakes Natl. Park), Canterbury (Harman Pass, Arthur’s Pass, Porters Pass), Sounds–Nelson (Richmond Ra.), Southern North Island (Tararua and Ruahine ranges) and Volcanic Plateau (Kaimanawa Ra., Atiamuri, Rotorua) EPs.
A medium- to high-elevation species. In forested areas it occurs on well-shaded rocky cliffs, while in penalpine communities it may be found, for example, in and at the edges of peaty, saturated bogs or between boulders. On Stewart Island (Mt. Rakeahua summit area, 600–690 m) present over a thick soil layer in a pocket between boulders in mosaic communities of penalpine cushion vegetation, herbfields, Chionochloa, prostrate Leptospermum scoparium, Olearia colensoi 0.5–2 m tall and significant areas of exposed rock. Also at the summit area of Te Rangaakapua (Urewera Natl. Park, Huiarau Ra., 1265–1320 m) occurring on the floor in open areas and on small banks of soil in open areas within mosaics of stunted Olearia colensoi and tussock with occasional Coprosma spp. Below the summit of “Little Moehau” (Coromandel Forest Park, ca. 800 m) the species formed a pure colony on the exposed side of a seepage area in a mosaic of Sphagnum bog and small communities of shrub-heath including Dracophyllum recurvum, Lepidothamnus laxifolius, Coprosma foetidissima, Oreobolus pectinatus, Corokia, and occasional stunted Weinmannia silvicola and Dacrydium cupressinum. In alpine communities it occurs over moist, peaty ground at edges of rills or tarns where it may form pure, compact colonies. Also over soil of protected pockets or of narrow crevices of boulders in areas of cliffs and outcrops with scattered alpine plants. The species often occurs as a pioneer over bare soil and the extensive, deep system of subterranean rhizoidous axes may be of significance in consolidating and stabilizing such habitats. In the bare soil niches often in pockets or under the lip of overhangs or under rock ledges, and, in such cases, at least a nominal amount of moisture and protection is provided. Also, in these niches Hygrolembidium acrocladum often is one of the few hepatics present. In wet peat-soil habitats it occurs with Allisonia cockaynei, Kurzia compacta, Marchantia foliacea and Solenostoma inundatum. In better-drained and bare soil sites it is found with Chrysoblastella chilensis, Ditrichum cylindricarpum, Notoligotrichum australe and Polytrichum juniperinum.
Comments : Similar to Hygrolembidium rigidum in the form of the leaf cells: non-elongated, chiefly 5–6-angled, with walls thin or at best very faintly firm-walled. Also approaching that species in the densely imbricate leaves, the shoots becoming stoutly julaceous and in its translucent light green to green color. Plants are at once distinct from H. rigidum in: 1) leaf cells much the same in size throughout the leaf; 2) leaf cells all (at least the epidermal) with 1–2 small, coarsely botryoidal oil-bodies; 3) surface of the leaves quite smooth, even distally; 4) leaves more nearly orbicular, never folded above; and 5) underleaves all small and appressed, the shoots never trigonous as seen in apical profile.
The underleaves although small are normally quite visible (Fig. 116: 5), but are sometimes inconspicuous and then appear as if altogether lacking. Shoots frequently have a mixture of conspicuous and inconspicuous underleaves. However, occasional shoots have underleaves uniformly reduced and thus, at first glance, appear underleaf-free.
Small phases of this species sometimes may be mistaken for Solenostoma totipapillosum, but the presence of underleaves and the lack of papillae on the stem will immediately distinguish Hygrolembidium acrocladum from that species.
