Hedwigidium Bruch & Schimp.

Description as per Hedwigidium integrifolium:

Plants medium-sized, gold-green above, dark brown or nearly black in lower portions, stoloniferous, forming mats on dry rock. Protonema globular, irregular in shape, mainly composed of rounded cells (fide de Luna 1990). Stems creeping, branching irregularly, with numerous microphyllous stolons arising from lower portions, in cross-section with incrassate outer cells grading into parenchymatous medullary cells, lacking a central strand. Rhizoids numerous, scattered on stems and stolons, smooth, brown. Shoots julaceous when dry. Leaves crowded and appressed when dry, spreading when moist, broadly ovate or oblong-ovate, acute at apex, cordate-auriculate at base, ecostate, with two plicae running close to margins from the base nearly to the apex, entire, narrowly but strongly recurved on both sides nearly to apex, 1.4–1.8(–2.1) × 0.65–0.8 mm; upper laminal cells more or less rectangular, with strongly sinuose and incrassate walls, mostly (9–)12–15 × c. 6 µm, with a few to several low and inconspicuous papillae on each surface, becoming longer (to c. 30 µm) in lower third of leaf; cells at leaf apex scarcely differing from those of upper lamina; central cells at leaf base gold-brown, more or less linear, less incrassate and less sinuose, forming a large and conspicuous group; marginal cells at base subquadrate in c. 12–15 rows extending far up the margins and gradually merging with the upper laminal cells; alar cells gold-brown or orange, forming a large but ill-defined group, sometimes slightly inflated. Microphyllous leaves (of stolons) tapered to a slender and attenuate apex.

Autoicous. Perichaetia terminal on stems or on short branches, the inner leaves oblong and acute, entire, c. 3.0 mm. Perigonia bud-like, c. 0.8 mm, lateral on branches and stems (sometimes <4 mm below perichaetia), the bracts ovate-acute, concave, pigmented, surrounding numerous antheridia and few filiform paraphyses. Setae c. 1 mm, straight; capsules immersed, erect and symmetric, broadly oblong-cylindric, c. 1.5 × 1.0 mm, lacking a differentiated neck, longitudinally sulcate, gymnostomous, narrowed slightly to the transverse mouth; exothecial cells mostly isodiametric to oblong, in distinct alternating bands of thin- and thick-walled cells; stomata few, superficial, restricted to extreme capsule base; annulus nil; operculum umbonate, broadly rounded at apex, c. 0.35 mm long × 0.7 mm diam. Calyptra mitrate and elongate, c. 1.5 mm, 3–4-lobed. Spores round, 27–33 µm, finely papillose-verrucate.

The separation of Hedwigidium from Hedwigia is supported by the morphological studies of de Luna (1995); his concepts are followed here.

Brotherus (1925, p. 70) considered Hedwigidium to contain two species, but Magill & van Rooy (1998) placed the South African H. erosum (Müll.Hal.) Paris into synonymy, effectively making the genus monotypic.

The status and typification of the genus Hedwigidium was discussed by Dalton et al. (2012). They considered Hedwigidium to be typified by the Irish H. imberbe (Sm.) Bruch & Schimp. and suggested that Hedwigidium be placed in synonymy with Braunia. If their synonymy is accepted, the nomenclatural implications for N.Z. material (which clearly does not belong to Hedwigia, as they suggest) are complicated and unclear. These problems are beyond the scope of this Flora, and are best resolved in a monographic context.