Pyrrhobryum Mitt.

Plants medium-sized to robust, tufted or forming turves. Stems erect, in cross-section ± angled, simple or much branched, in cross-section with a central strand and thick-walled cortical cells. Leaves uniform or sometimes dimorphic (in P. bifarium). Stem leaves distributed around stem, spreading, linear-lanceolate, linear, or ovate-lanceolate, often acuminate, often decurrent, bistratose and mostly plane at margins, sometimes becoming scale-like near stem base. Branch leaves differing in some species (in P. bifarium), then more ovate-lanceolate and shorter than stem leaves, bifarious, somewhat asymmetric at base. Upper laminal cells of stem and branch leaves smooth, firm-walled, mostly oblong, ± isodiametric, or oblate, often somewhat irregular; marginal cells bistratose and often forming wings (best viewed in cross-section), not elongate; alar cells not differentiated. Costa fading in acumen or excurrent, bearing abaxial spines above, in cross-section with median guide cells and abaxial and adaxial stereids.

Dioicous (in N.Z. species) or autoicous. Perichaetia lateral and scattered on stems or in basal clusters. Perigonia budlike, mostly scattered on lower stems, with filiform paraphyses. Setae elongate, straight or flexuose; capsules inclined or horizontal, oblong-cylindric or obovate, asymmetric, with a weakly defined neck, constricted below the mouth when dry; exothecial cells mostly irregular, with firm or thin walls; annulus vesicular and persistent in N.Z. species; operculum conic, often rostrate. Peristome double and well-developed; exostome teeth yellow-brown, narrowly lanceolate, bordered, outer surface transversely striate in lower half, baculate above, inner surface lamellate; endostome from a high membrane; segments as long as teeth, keeled, widely or weakly perforate; cilia in groups of 1–3, nodose. Calyptra cucullate. Spores spherical, finely papillose.

Mitten's concept of Pyrrhobryum received little application until 1980 when Manuel (1980) focused attention on the heterogeneity of Brotherus’ concept of Rhizogonium. Manuel amended Mitten’s concept of Pyrrhobryum to include only species with radially disposed leaves, multistratose, doubly-toothed margins, abaxially spined costae, and distinctly necked capsules. Koponen et al. (1986) noted that some species included within Manuel’s concept of Pyrrhobryum (e.g., P. bifarium) can have distichous leaves, and proposed that a more meaningful classification would utilise the length of the marginal cells (short in Pyrrhobryum vs elongate in those species of Rhizogonium in which a border occurs) and de-emphasise the insertion pattern of the leaves.

Manuel’s generic concept is adopted here. Pyrrhobryum paramattense was placed by Manuel in section Pyrrhobryum (characterised by basal perichaetia). It is clearly closely allied to the generitype. Pyrrhobryum bifarium and P. mnioides s.l. were placed by him in the section Bifariella (characterised by lateral perichaetia).

Alternative generic and family placements for two of the Pyrrhobryum species occurring in N.Z. have recently been proposed. Bell et al. (2007) transferred P. bifarium and P. mnioides to the genus Hymenodontopsis Herzog, which is founded on the Malesian H. stresemannii Herzog. The species occurs in New Guinea and was treated for the Huon Peninsula by Koponen et al. (1986). In addition to the transfer of N.Z. species to Hymenodontopsis, the molecular phylogeny presented by Bell et al. places the genus in a clade with Aulacomnium androgynum (only the type species of Aulacomnium was sampled) and two species of the Australian genus Mesochaete. They treat this clade as the Aulacomniaceae. Their phylogeny is based on four genes derived from both chloroplast and mitochondrial genomes and is presented as a strict consensus tree based on 16 most probable topologies.

There is a lack of congruence between their molecular data and morphology. Considering the transfer of N.Z. taxa to Hymenodontopis: H. stresemannii from Malesia (CHR 352062) has erect, symmetric, cupulate, and very short (c. 1.0 × 0.8 mm) capsules with very long (c. 2.0 mm) and slenderly rostrate opercula (c. two to three times the urn). The peristome is single and consists of a low endostomal membrane with short and irregular projecting segments. There is no annulus. The endostomal nature of the H. stresemannii peristome was confirmed by Shaw & Anderson (1986). The capsules of the two N.Z. species allegedly congeneric with this species differ strongly from it in their sporophyte morphology. P. bifarium has horizontal, asymmetric, and obovate capsules, with a conic operculum. The peristome is well-developed and double with a high endostomal membrane, keeled segments, and nodose cilia; there is a differentiated vesicular annulus. New Zealand material of P. mnioides subsp. contortum likewise has horizontal, asymmetric, and obovate capsules albeit with a stoutly rostrate operculum that is c. half the urn in length. The peristome here is well-developed and double with a high endostomal membrane, well-developed keeled segments and nodose cilia. Its annulus is also vesicular and persistent. These two N.Z. taxa differ markedly in capsule morphology from H. steresmannii and the proposed transfer of these species to Hymenodontopsis is therefore not accepted here. Material of the South African P. vallis-gratiae (Müll.Hal.) Manuel (also transferred to Hymenodontopsis by Bell et al. 2007) has not been seen. While Pyrrhobryum as presently circumscribed is probably heterogeneous (polyphyletic), further study is required to clarify the relationships of its component species. The conservative generic assignments advocated here accord with those of Gilmore (2006) and are similar to those of Koponen et al. (1986).