Campyliadelphus polygamus (Schimp.) Kanda

Plants gold- or brown-green. Stems irregularly branched, to at least 25 mm long, in cross-section with 2 layers of thick-walled cortical cells and a distinct central strand; sparsely beset with scattered fascicles of smooth, red-brown rhizoids. Stem leaves erect-spreading below, often distinctly secund (in N.Z. material), ovate-lanceolate, not complanate, c. 1.8–2.0(–2.3) × 0.6–0.8 mm (not flattened), clasping or sometimes weakly decurrent at base, ± abruptly tapered to a channelled and often spirally twisted acumen, entire and plane at margins; mid laminal cells linear, slightly vermicular, (45–)60–72(–90) × 5–8 µm, somewhat longer near costa, not porose, lumina much wider than the cell walls; alar cells forming a large, ± triangular group extending nearly to the costa base, numerous, moderately inflated, firm-walled, mostly oblong, hyaline or weakly pigmented, surrounded by an ill-defined area of many smaller, firm-walled, supra-alar cells. Costa single, thin and inconspicuous above, mostly ¼–½ the leaf length. Branch leaves shorter and narrower, mostly 1.2–1.4 × 0.25–0.35 mm, and with a smaller alar group. Pseudoparaphyllia present but not clearly seen.

Autoicous. Perichaetia scattered on stems, c. 5 mm long, the inner leaves erect, c. 3–4 mm, narrowly lanceolate with a narrowly filiform apex, entire, costate, plicate, and sheathing. Perigonia inconspicuous on stems. Setae straight or ± flexuose, c. 20–30 mm, yellow-brown, smooth; capsules cylindric, strongly curved, c. (2.5–)3 mm long with a well-defined and tapered neck; mouth oblique, narrowed when dry; exothecial cells firm-walled, oblong to nearly rectangular; stomata with elliptic pores; annulus differentiated (not clearly seen); operculum conic and blunt at apex. Peristome as per genus; with appendiculate cilia in groups of three. Spores mostly 15–18 µm, papillose (seen in few collections).

Kanda 1976, fig. 27, 13–24; Crum & Anderson 1981, fig. 462 (as Campylium polygamum); Smith 2004, fig. 257, 1–4 (as Drepanocladus polygamus).

The inflated alar cells, laminal cell morphology and dimensions, the leaf shape and their channelled acumens (seen both moist and dry), a well-developed single costa, and autoicous sexuality all facilitate recognition. Campyliadelphus polygamus is a more delicate plant with narrower leaves and usually less pigmentation than C. stellatus. The N.Z. material studied most closely has been autoicous and this agrees with the statements of both Sainsbury (1955) and Kanda (1976, p. 267 et seq.); it is unclear whether N.Z. material is "polygamous" as the species is stated to be in some parts of its range.

Campyliadelphus polygamus is very easily confused with Leptodictyum riparium, a species which often occupies similar habitats, and not all material can be distinguished with confidence. The leaves in C. polygamus are more abruptly constricted and with distinctly channelled acumens; these contrast with the ± evenly tapered and flat upper leaves of the Leptodictyum. Both species can have spirally twisted leaves, but this is not constant and is less distinct in C. polygamus. Additionally, the plants of C. polygamus are not complanate, the leaves smaller, the costa shorter (less than half the leaf length) and the mid laminal cells slightly shorter than those of L. riparium. Campyliadelphus polygamus occurs from lowland to alpine elevations, whereas L. riparium is confined to lowland situations.

Extremely broad in its habitat requirements; often aquatic or nearly so. This species is documented from areas of a wide range of bedrock types, including schist, limestone, marble, and cation-rich volcanic bedrock. Occurring on both peaty and mineral soils in fens, river and lake margins, raupo-dominated swamps, and occasionally pakihi. Also in wet alpine herb fields (as at Mt Ruapehu, Wellington L.D.), in high elevation Schoenus pauciflorus dominated flushes (as at Malte Brun Range, Canterbury L.D.), in wet red-tussock grassland (as at Strath Taieri, Otago L.D.), and cushion bogs (as at Mavora Lakes, Southland L.D.). Bryological associates include Breutelia pendula, Bryum pseudotriquetrum, Drepanocladus aduncus s.l., Meesia uliginosa, and Philonotis tenuis. Occurring from near sea level to 1620 m (Mt Ruapehu).

There is a tendency in some N.Z. populations for the stem leaves to become secund. It is unclear whether this variability is reflected in material from other southern hemisphere regions. It is inappropriate to attempt to recognise secund populations at any infra-specific level, although a number of varieties and forms of C. polygamus have been previously recognised, particularly in Europe.

Crum & Anderson (1981, p. 951) considered C. polygamus to be a "not very well defined [species]" and thought some forms of it showed "a curious resemblance to straight-leaved expressions of Drepanocladus aduncus." Hedenäs (1997) proposed placement in the genus Drepanocladus on primarily morphological grounds.