Barbula is a genus of mosses belonging to the family Pottiaceae, order Pottiales, within the class Bryopsida (true mosses). The genus is cosmopolitan, occurring on every continent, with species growing primarily on soil and rock surfaces, particularly favouring calcareous substrates.
Plants are typically small and inconspicuous, ranging from about 0.5 to 3 cm in height, growing erect with well-defined stems that commonly form dense cushions or mats. Leaves are mostly lanceolate in shape, sometimes tongue-shaped, and in dry conditions lie straight or gently curved rather than crisped. The midrib (costa) extends to the leaf tip or is shortly excurrent but does not form a glassy hair point. Upper leaf cells are rounded to quadrate and appear dull green, while lower cells are rectangular. The spore capsule is cylindrical and erect, borne on a long yellowish or reddish seta. A distinctive feature is the peristome — the ring of tooth-like structures surrounding the capsule mouth — which bears long, typically twisted teeth. Many species also reproduce vegetatively through rhizoid gemmae.
The boundaries of Barbula have long been debated. In the broad sense the genus once encompassed more than 300 species worldwide, but molecular and morphological studies have led to the separation of several satellite genera, most notably Didymodon and Pseudocrossidium, on the basis of peristome structure, midrib characters, and DNA data. In the strict sense Barbula comprises approximately 200 species, though the genus is considered by some authorities to be polyphyletic, meaning it does not represent a single natural lineage. GBIF currently recognises 23 species within the genus under its backbone taxonomy.
Well-known representatives include Barbula unguiculata, a common species of disturbed ground and calcareous soils across Europe, and Barbula convoluta, also widespread in temperate regions.
Etymology
The genus name Barbula is Latin for "little beard," an allusion to the long, twisted teeth of the peristome surrounding the spore capsule. The corresponding German vernacular name, Bärtchenmoose, carries the same meaning.
Distribution
Barbula has a cosmopolitan distribution, occurring on every continent. Most species grow on bare soil or rock surfaces; many are strongly associated with calcareous (lime-rich) substrates including limestone, mortar, and chalk-derived soils.
Ecology
Species of Barbula are pioneers and colonisers of disturbed, open habitats. They are often found on compacted or bare soil, walls, paths, rock faces, and rubble, with a clear preference for calcareous or base-rich substrates. Many species tolerate desiccation and can rehydrate rapidly after rain. Vegetative reproduction via rhizoid gemmae is common alongside spore dispersal.
Taxonomy Notes
Barbula belongs to the family Pottiaceae, one of the largest moss families, within the order Pottiales. The genus circumscription is contested: in the broad sense it included over 300 species worldwide, but molecular phylogenetic studies have demonstrated that it is probably polyphyletic. Genera including Didymodon and Pseudocrossidium have been segregated on the basis of peristome morphology, costa characters, and molecular evidence. In the strict sense following Stech & Frey, Barbula comprises around 200 species globally. GBIF currently recognises 23 accepted species under the genus in its backbone taxonomy.
