Hygrolembidium rigidum R.M.Schust. & J.J.Engel
Hygrolembidium rigidum R.M.Schust. & J.J.Engel, Phytologia 62: 9. 1987.
Holotype: New Zealand, South Is., Fiordland Natl. Park, Mt. Burns, Hunter Mtns., 4500–5000 ft., Schuster 84-101 (F); isotype: (CHR).
Plants fleshy and brittle, subisophyllous or underleaves only moderately smaller than leaves on the erect, ± triquetrous shoots, intense pure green, the leafy shoots to 1.8 mm wide. Branching common, the branches mostly ventral-intercalary, occasionally lateral-intercalary, very rarely of Frullania type; stolons sporadic or occasional, colorless, only rarely forming a freely branched prostrate system from which arise the erect leafy shoots. Stem very thick for plant size, formed of up to ca. 50 rows of cortical cells that are thin-walled (except free walls faintly thickened), variable but rather small. Rhizoids occasionally toward base of erect, leafy shoots, from basal cells of underleaf or leaf or from stem at immediate base of foliar tissue. Leaves firm, rigid, opaque, often ± keeled below, polystratose over 0.6–0.8 their area, only marginal and distal sectors unistratose; leaves in cross section toward base (2)3–4-stratose in intramarginal sector, the leaves remaining polystratose to at most within 2 cells of margin, the marginal sector unistratose, the epidermal cells of leaf averaging ± the same size as internal cells; leaves contiguous to moderately imbricate, widely spreading, transverse to feebly succubously inserted, deeply concave to subcupulate to subcanaliculate, broadly ovate-triangular to reniform-orbicular to oblate, 860–1525 µm wide × 665–1155 µm long when flattened; apex somewhat narrowed, usually with a sharp, short incision or at least retuse, sometimes 3–4-lobulate and/or dentate, often loosely folded or canaliculate; lamina margins entire or often repand to repand-dentate, slime papillae frequent. Cells showing gross size increase from apical and marginal areas (here 20–25 × 24–30 µm to 24–35 × 28–48 µm) to base (here 40–60 × 55–85 µm to 60–85 × 70–100 µm up to 45–60 × 100–120 µm); cell walls thin throughout, distally with at most medium-sized trigones; surface obscurely to distinctly papillose throughout leaf, only the median or median-basal cells sometimes smooth. Oil-bodies completely lacking, only a few scattered, tiny, glistening oil-droplets present. Chloroplasts numerous, small: 1.4–2.4 × 2.4–4.3 µm. Underleaves 0.4–0.65(0.75) as large as leaves, ovate-triangular to orbicular-reniform to broadly ovate-reniform, usually folded-canaliculate; apex often retuse or shallowly bifid; lamina margins entire or repand, often with slime papillae.
Androecia on both lateral- and ventral-intercalary branches; bracts erect, the apex crenate-denticulate; antheridia single per bract, the stalk bistratose throughout or unistratose but with bistratose areas. Gynoecia mostly ventral in origin, occasionally lateral; bracts and bracteoles nearly identical (except bracts somewhat falcate), sheathing only basal ca. 0.25 of perianth and appressed to the perianth except for the slightly patent tips, somewhat larger than leaves, concave, ovate from a broad base, the apex blunt to narrowly truncate or subacute, unlobed, with armature as in perianth mouth; lamina margins dentate to ciliate, slime papillae common. Perianth exceptionally long for plant size, to 6 mm long × 1.2 mm in diam., long-fusiform, cylindrical below and bluntly 3(4)-gonous above, the mouth crenate-denticulate with thin-walled, laterally connate, finger-like cells that are mostly 3.5–5:1 and 10–18 × 45–55(65) µm; perianth 3–5(6)-stratose at base.
Seta with 10–14 rows of epidermal cells. Capsule long-ellipsoidal (2.6–3.5× as long as wide), the wall 3(very locally 4)-stratose, 46–48 µm thick; outer layer of cells with longitudinal and some transverse walls with thin to moderately thickened continuous sheets of wall material but with nodular thickenings weak or lacking (primary walls with thickenings often weaker or absent); innermost layer of cells with radial (vertical) bands nodular to spur-like in surface view, varyingly extended tangentially to form incomplete to complete, semiannular bands.
Spores 12.4–13.5 µm in diam., the wall yellow-brown, with low, delicate papillose and simple or sometimes furcate vermiculate markings, 1.3–1.5× the elater diam. Elaters faintly tortuous, bispiral, 8.6–9.6 µm wide, the spirals 2.9–3.8 µm wide.
Distribution and Ecology : Endemic to New Zealand: South Island (660–1330 m). Known from Fiordland, Westland and Western Nelson (Paparoa Ra., Stockton and Denniston plateaus, Cobb Valley) EPs.
The species typically occurs in penalpine areas of Dracophyllum and Olearia colensoi scrub or Hebe and Dracophyllum scrub or in Chionochloa pallens – C. flavescens or C. rubra tussockland. In both scrub and tussockland it occurs over soil at bases of boulders, under overhangs, in pockets, as well as under tussock blade cover. Here it occurs, characteristically, with Pachyschistochila. Other accompanying species are Andreaea acutifolia, Campylopus clavatus, Chloranthelia berggrenii, Cladia retipora, Cladonia confusa, Dicranoloma robustum, Jamesoniella colorata, Kurzia hippuroides, Pleuridium arnoldii, Racomitrium crispulum, Rhizocarpon geographicum, Riccardia cochleata, Siphula fragilis, Solenostoma totipapillosum and Verdoornia succulenta. The species rarely occurs in Nothofagus forests (near South Branch of Borland Burn, Fiordland, 855–870 m) on soil of a bank above a cascading stream.
Comments : Distinctive for this species are the 1) very large basal epidermal leaf cells, contrasted to the much smaller distal cells; 2) lack of oil-bodies; 3) very thick and rigid stem; 4) lack of differentiation of epidermal and internal leaf cells as seen in leaf cross section; 5) frequently rather large underleaves, often similar to the leaves, so that the shoot is almost trigonous when looking down on the apex; and 6) unusually elongated, long-tapered and fusiform perianth, which, in contrast to the fleshy stem and leaves, is exceptionally thin and delicate above, on old plants typically collapsed and browned. The thin and delicate, unusually small bracts and bracteoles are unlobed, edentate and somewhat asymmetrically ovate-pointed from a broad base. The species usually occurs in better-drained, less peaty habitats than Hygrolembidium australe and H. acrocladum. The species resembles a small Pachyschistochila but has larger underleaves than any species in that genus.
