Blindia robusta Hampe

Plants yellow-green, gold-green to nearly black in submerged forms, glossy. Stems wiry, commonly 40–70 mm, moderately branched by subperigonial innovation (possibly also by forking), in cross-section with thick-walled cortical cells and a small but distinct central strand, with fragments of leaf bases adhering after leaves are removed. Leaves mostly falcate to flexuose-secund or ± straight when dry, mostly nearly circinate at stem apices, similar when moist, subtubulose, narrowly lanceolate-acuminate, lacking distinct shoulders, evenly tapered to a long, fine, and entire subula, clasping and ± auriculate at base, with lamina extending c. ⅓ (rarely c. ½) the leaf length (viewed under stereoscope), (5–)6–9 × (0.3–)0.4–0.55(–0.9) mm (when flattened); upper laminal cells (c. ⅓ above insertion) linear and ± straight, unistratose, strongly incrassate (the walls equal to or wider than the lumina), c. 36–60 × 3 µm, slightly expanded at cell ends; lower laminal cells longer, to c. 100 µm, and becoming moderately porose; alar cells mostly inflated and thinner-walled, pigmented, forming a well-defined, clasping, and ± auriculate group, usually extending 5–8 cells up the leaf and there merging abruptly with the laminal cells, separated from the costa by elongate cells, occasionally poorly differentiated and differentiation often variable on a single stem. Costa c. 50–60(–110) µm wide near base, well-defined and filling the subula, in cross-section with a median layer of guide cells (c. ⅓ above base).

Autoicous or sometimes dioicous. Perichaetia terminating the stem but usually overtopped by innovation; perichaetial leaves from a broadly oblong and sheathing base, abruptly shouldered and narrowed to a long and flexuose subula. Perigonia rather large, in autoicous plants below the perichaetia, either very close (c. ≤1 mm) or separated by up to 9 mm; in male plants terminal and generally overtopped by innovations; inner perigonial bracts short (c. 1.0–1.5 mm) and strongly shouldered, lacking a long subula. Setae (8–)10–16 mm, flexuose-erect, stout, twisted to the right when dry, little altered when moist, orange; capsules urceolate or turbinate and wide-mouthed when dry, turbinate to ± hemispheric when moist, long-exserted, yellow- or red-brown, pachydermous, (0.8–)1.0–1.5 × 0.8–1.2 mm; exothecial cells irregular in shape and size, incrassate and weakly collenchymatous, c. 3–4 rows thicker-walled and more regularly isodiametric to ± oblate at rim, 1–2 rows there often hyaline; stomata apparently absent; operculum long-rostrate from a weakly conic base, oblique, equal or somewhat longer than the urn, systylious. Peristome well-developed but often broken, red-brown, the 16 teeth broadly lanceolate, irregularly divided and ± cribose above, the outer surface often appearing densely and coarsely cribose-warty near base (apparently due to preperistome development) and papillose above, the inner surface with a median line but otherwise smooth (very difficult to see). Spores 27–45 µm, smooth, green.

Bartlett & Vitt 1986, figs. 75–83, 146, 152, 157; Malcolm & Malcolm 2003, p. 6; Seppelt 2004, fig. 100.

The ± straight-leaved forms discussed above are most likely to be confused with B. lewinskyae, especially in the absence of capsules. The somewhat shorter leaves of even the extreme forms of B. robusta help to separate these species; when capsules are present confusion is impossible.

Sterile material of falcate-leaved forms of B. robusta could be confused with species of Drepanocladus or Warnstorfia. However, in B. robusta the leaves are much finer, with the subulae filled by the costae, and the stems more wiry than in any species of Drepanocladus or Warnstorfia. The manner in which the leaf base fragments adhere to the wiry stems provides additional distinction, as do the generally more distinctly pigmented and auriculate alar cells.

Most common and best developed at the margins of small subalpine and alpine streams and in seepages. Often associated with late snow beds and less commonly with waterfall margins. A large fraction of herbarium collections are from granite-derived gravels, but it also occurs on larger rocks, as well as coal faces and peaty or silt soils. It can grow in pools in Sphagnum-dominated bogs (as at Mt Anglem, Stewart I.) and in tarns, as well as Empodisma minus-dominated flushes. It is usually not deeply submerged. Associated with a wide-range of non-calcareous rock types. Frequently associated mosses include Blindia magellanica, Calliergon sarmentosum, and Sphagnum falcatulum. Ranging on North I. from c. 1220 to 1725 m (both on Mt Ruapehu) and on South I. from 540 (Denniston Plateau, Nelson L.D.) to c. 1890 m (Remarkable Range). On Stewart I. it occurs from sea level upwards.

On Mt Tongariro it occurs shallowly submerged in water of pH between 3 and 5 on rocks at the margin of Blue Lake at 1725 m elevation. It also occurs in circumneutral water in Lower Tama Lake, in Tongariro N.P. (L. Roberts, pers. comm., 28 May 2010).

When well-developed and fertile, the long, finely subulate and falcate to circinate leaves, the erect-flexuose and rather stout setae bearing exserted capsules make this widespread and common species unlikely to be mistaken.

However, B. robusta shows considerable morphological variability. In a small fraction of aberrant collections from the South I., the leaves are weakly secund to ± straight. In such plants the overall coloration is dark green to nearly black, the leaves near the upper end of continuous variation for length (c. 7.0–9.0 mm), and wider than usual at the insertion (to c. 0.7–0.9 mm). Such plants generally occur in slow-moving small streams. Similar material but with moderately secund leaves occurs on Stewart I. William Martin (in herb.) termed it "the usual form on most Stewart Island Mountains". In such Stewart I. and South I. material the alar cell fragments remaining attached to the removed leaves are quite variable. The alar group may be pigmented and form a well-defined, clasping, and ± auriculate group (as in A.J. Fife 5456 from Mt Priestly, Nelson L.D.), hyaline in a large auriculate group that is visible in nearly all leaves (as in J. Child 6670 from "Ajax Swamp" near Mt Pye, Otago L.D.), or mostly absent (as in A.J. Fife 9563 from Percy Stream, Southland L.D., CHR 477529). When a large number of collections are viewed, a range of variability suggestive of an ecological cline is observable. Material growing in slow-moving or stagnant water is usually sterile. In some populations of slow-moving water (as in A.J. Fife 5456) the costae are broader (to c. 110 µm) and less clearly defined than usual. Bartlett & Vitt (1986, p. 226) considered basal costal width to extend to 150 µm in this variable species. They concluded that "the falcate-secund habit of the leaves is … variable, as is the width of the leaves and their manner of insertion".

As noted by Bartlett & Vitt (1986, p. 225), the frequency with which the operculum remains attached to the columella in this species varies, but this variability does not seem to correlate with any habitat or geographic feature. It is possible that some of this variability is merely a function of capsule age.