Hygrolembidium triquetrum J.J.Engel & R.M.Schust.
Hygrolembidium triquetrum J.J.Engel & R.M.Schust. in Schuster and Engel, Phytologia 62: 11. 1987.
Holotype: New Zealand, South Is., Westland Prov., Mt. Aspiring Natl. Park, below and W of Mt. Armstrong, SSW of Mt. Brewster, 1250–1450 m, Engel 17790 (F); isotype: (CHR).
Plants exceedingly fleshy and brittle, subisophyllous to ± isophyllous on the erect triquetrous shoots, pure green, the leafy shoots to 2.4 mm wide. Branching copious, both ventral- and lateral-intercalary; stolons colorless, common but not usually forming a freely branched prostrate system. Erect leafy shoots arising from stolons. Stem very thick for plant size, the cortex in ca. 65 rows of thin-walled cells, well differentiated, in 1 or locally 2 layers; medullary cells variable, distinctly larger than cortical cells. Rhizoids often 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, brittle, opaque, often ± keeled below, very firmly attached at a thickened, fleshy base, polystratose for ca. 0.85 their area, only a few cell rows of marginal sector and several of distal sector unistratose; leaves in cross section toward base 5–7-stratose in intramarginal sector, the epidermal cells of leaf averaging considerably smaller than internal cells, those of abaxial face particularly so; leaves contiguous to moderately imbricate, orientation variable: suberect to widely spreading, transverse to faintly succubously inserted, moderately concave to cupulate to canaliculate, oblate to reniform, 1125–1225 µm wide × 850–900 µm long (to base of abaxial face) when flattened; apex variable, often broadly rounded to subtruncate, at times somewhat narrowed (particularly on smaller leafy branches), entire or sometimes with a few small teeth, sporadically retuse; lamina margins entire or often repand to repand-dentate, slime papillae frequent. Cell walls thin to slightly thickened, those of apical sector with at most medium-sized trigones, those toward base leptodermous, with trigones small or absent; cells of apical sector subquadrate, 23–31 µm wide and long; median cells 22–31 µm wide, 26–37(42) µm long; basal cells variable in shape: some short-rectangular or even subquadrate, others elongate, the cells 22–32 µm wide, 36–52 µm long; surface uniformly smooth. Oil-bodies not seen. Underleaves similar to leaves in form and often not or hardly differentiated from them, 0.5–0.75 as large as leaves to at times subequal to them, ovate to subreniform; apex plane to (often) hood-like, variable, undivided and entire or retuse to shallowly bifid; lamina margins entire or repand-dentate to dentate, often with slime papillae.
Androecia on both lateral- and ventral-intercalary branches, subjulaceous, vermiform, tiny for plant size, only 385–525 µm wide, colorless but with whitish antheridia, fragile and easily detached, often crowded toward base of erect, leafy shoots, also present (but less crowded) on stolons; bracts with apices and sides suberect, the apices crenate-denticulate; antheridia single per bract, the stalk biseriate. Gynoecia not seen.
Distribution and Ecology : Endemic to New Zealand: Stewart Island (530 m), South Island (1250–1730 m). Known only from Rakiura and Westland EPs.
Known from a few localities. At the Mt. Rocky summit area on Stewart Island plants occurred over soil protected by a rock ledge in mosaic communities of dense heath-forming shrubs to 3 m tall, herbs and dwarf heaths to 0.5 m tall, dominated by stunted Leptospermum scoparium and Dracophyllum and a ground tier including Empodisma minus. The type occurred in a very compact, dense mat mixed with Pachyschistochila cf. childii on soil of an ice-scoured slope in the alpine zone. In the Young Ra. (Aspiring Natl. Park) it was found on peaty soil in snowmelt seepage in Marsippospermum gracile and Poa colensoi grassland with Cephaloziella sp., Ditrichum difficile, Gaultheria novae-zelandiae var. depressa, Pachyschistochila subhyalina and Polytrichastrum alpinum.
Comments : The subisophyllous to ± isophyllous, erect, triquetrous shoots are distinctive, even in the field (Fig. 114: 1–4). Leaves are fleshy and in basal cross section are 5–7-stratose, with the epidermal cells averaging smaller in diameter than the internal cells (Fig. 114: 5, 6). The cell width notably remains nearly the same from leaf apex to base, 21–32 µm (Fig. 115: 3). The species is closely allied to Hygrolembidium rigidum and the two are placed in a separate section of their own, sect. Rigidae.
