Cratoneuropsis (Broth.) M.Fleisch.

Cratoneuropsis is treated here as a genus with one highly variable species.

Brotherus (1901–1909) initially described Cratoneuropsis as a section within Campylium, but subsequently (Brotherus 1925) followed Fleischer by recognising it at the generic level. Brotherus (1925, p. 334) used the robustness of the plants, degree of leaf reflexion, subtle differences in the shape of the leaf base, and ill-defined features of costal thickness and length to differentiate three, predominantly Australasian, species. Brotherus’ segregate species are not accepted here.

Dixon (1929, p. 320) retained Cratoneuropsis relaxa within a broadly-defined Campylium, while subsequent Australasian workers (e.g., Sainsbury 1955; Scott & Stone 1976) have recognised the genus, while expressing concern about the extreme variability of C. relaxa.

There is no consensus among modern workers as to the limits of Campylium, Campyliadelphus, and allied genera (see Kanda 1976; Buck 1998; Hedenäs 2003).

It is not uncommon for moss species subject to prolonged or permanent immersion to exhibit dramatically differing growth forms. The remarkable environmentally-induced plasticity of C. relaxa makes its circumscription using morphological characters alone exceedingly difficult. This plasticity has led to the formal taxonomic description of several superfluous taxa, at species, genus, and even family rank.

At risk of oversimplification, Cratoneuropsis relaxa in N.Z. has four intergrading growth forms. The growth forms are correlated with different water relations, including constancy of irrigation and degree of immersion. The four growth forms are here termed, for convenience, the "relaxa" growth form, the "decussata" growth form, the "sciaromium" growth form, and the "hypnobartlettia" growth form. The "relaxa" growth form is associated with strongly and persistently irrigated habitats. It is the most common growth form in N.Z. and is the variant of Cratoneuropsis relaxa usually illustrated in regional Australasian floras. The "decussata" growth form is more delicate and associated with drier and calcareous rock substrates. The "sciaromium" growth form is associated with permanent or near permanent immersion in flowing water. The "hypnobartlettia" growth form is associated with permanent immersion in deep, moving water of great optical clarity and has been found only at Te Waikoropupū Springs in Nelson L.D.

I have not attempted to encompass the morphological variations of the "sciaromium" growth form or the "hypnobartlettia" growth form in the following description; such a broadened description would, in my opinion, not be useful.

Because of the high level of interest (and the associated formal taxonomic descriptions) given to the environmental variants of C. relaxa over many decades, the four growth forms are each discussed below, with supplementary morphological and distribution notes.

Ochyra et al. (2008) recorded and illustrated what they termed Cratoneuropsis relaxa subsp. minor (Wilson & Hook.f.) Ochyra from the Macquarie, Campbell, and Auckland Is, as well as mainland Antarctica, Patagonia, South Shetland Is, Falkland Is, South Georgia, and other subantarctic islands. The basionym of this name, Hypnum filicinum var. minus Hook.f. & Wilson, has an Auckland I. type, but it has not been available for examination. Given the very great plasticity of C. relaxa s.l. in N.Z., I doubt very much that Ochyra’s subsp. minor, as occurring on southern offshore islands of N.Z., is worthy of taxonomic segregation. In many respects Ochyra’s subsp. minor is suggestive of what is here treated as the "sciaromium" growth form of C. relaxa. However, because the type has not been examined, it is neither included in the above synonymy nor discussed further here.

Cratoneuropsis subrelaxa (Broth.) Broth. is a name applied to some material from eastern Australia; to my knowledge this name has not been used for N.Z. collections. It was not considered by Scott & Stone (1976) and is not considered further here.