Gertrudiella Broth.

The description of Gertrudiella torquata, below, is presented here as representative of the genus.

Plants yellow-brown or yellow-green above, dull brown below, in dense tufts or turves, or gregarious. Stems 5–25(–35) mm, branched, in cross-section with a central strand and well-developed sclerodermis. Leaves erect-spreading from a weakly sheathing base when moist, individually twisted and stiffly twisted around the stem to form a rope-like shoot, but often with some apices spreading (especially at the shoot apex) when dry, (1.0–)1.5–3.0 mm, lanceolate, carinate, narrowly obtuse, acute or acuminate; margins narrowly recurved to revolute, unistratose, crenulate by bulging cells and low, rounded papillae; upper laminal cells clear in outline, irregularly rounded-quadrate, thick-walled, bulging, weakly to conspicuously papillose with 1–2 simple or complex papillae, c. 6–8 × 6–8 µm, becoming oblate towards the margin and longer towards the leaf base; lower laminal cells often little differentiated, firm-walled, not hyaline, smooth, rectangular medially, becoming shorter towards the leaf margins, where 1 or more rows are ± quadrate. Costa reddish or concolorous, stout, percurrent or excurrent as a sharp or blunt arista; adaxial superficial cells similar to adjacent laminal cells throughout; abaxial superficial cells quadrate to short-rectangular distally. Axillary hairs of 3–5 cells, with the basal cell shorter and brown. Laminal KOH colour reaction yellow-orange.

Dioicous. Perichaetia terminal, with perichaetial leaves erect and loosely sheathing the seta base, similar in size and shape to vegetative leaves, or with a longer and more acuminate apex, and with a basal zone of lax, elongate cells, which may extend for the entire lamina in the innermost perichaetial leaf. Perigonia terminal (with innovative shoot produced from below), bulbiform. Setae slender, flexuose, dark red below, paler above, 9–20 mm. Capsules erect, narrowly cylindric and slightly curved, 1.75–2.0 mm. Operculum bluntly and obliquely rostrate, with cells spiralled, c. ½ the theca length. Peristome long (c. 1 mm at dehiscence), spiralled approximately twice, of 16 pale teeth each divided into 2 densely spiculose filiform rami, arising from a low, fenestrate basal cylinder. Calyptra cucullate. Spores 6–10 µm, smooth.

The genus Gertrudiella was regarded as monotypic by Zander (1993)​​​​​​​, its sole representative being the Bolivian G. uncinicoma (as G. validinervis). On the basis of sequencing data from both nuclear and chloroplast DNA of 122 species of Didymodon and allied genera (Jiménez et al. 2022​​​​​​​), a distinct clade was resolved that included Gertrudiella uncinicoma and nine species of Didymodon. Fifteen new combinations were made in Gertrudiella, including a single Australasian species, Didymodon torquatus.