ASCOMYCOTA | EUROTIOMYCETES > VERRUCARIALES > Verrucariaceae

Verrucariaceae is a large, complex family with a wide variety of species, which are placed in 27 genera on the current British List. Many include taxa with squamulose or foliose thalli, which are not the subject here, as this page is primarily for unidentified saxicolous crustose species found in urban, rather than coastal habitats. Family keys separate the taxa according to the ascospores, which in most cases need to be microscopically examined in order to determine the species or possibly even the genus. They are further separated into three main habitat types, broadly defined as marine (coastal), freshwater (semi-aquatic) and terrestrial.

After repeatedly being advised that members of this family cannot be reliably identified in the field or visually from photos, I thought it would be useful to go through the list to get a better understanding of the genera and the species that are likely to be encountered even if they can't be identified. Concentrating purely on the more common inland terrestrial species that are known to occur locally, there are essentially just three genera that need to be considered; Verrucaria, Bagliettoa, and Thelidium.   

The main characteristic feature of these species is their more or less spherical or flask-shaped perithecia with a single opening, otherwise completely enclosed within a well-developed involucrellum.

Verrucaria, the type genus, includes fifty plus species, many of which occur only in marine or freshwater habitats, and a very large number that are either rare or very poorly recorded. Referencing the distribution maps shows that there are only a small number of species that would realistically need to be considered:

V.dolosa, with small perithecia; on silicious and limestone rocks, concrete or brick, tolerant of shade,

V.elaeina, one of the few species that can be visually identified - see separate account (graded 2/5),

V.hochstetteri, common on calcareous rock; another species that can often be recognised, in this case by the immersed thallus and large perithecia sunken in pits (graded 2/5),

V.macrostoma, common on limestone, mortar and calcareous sandstone in semi-natural habitats; with a typically pale to mid-brown thallus, darker when exposed (graded 2/5),

V.muralis, common in various urban environments on limestone, mortar and brick, also on pebbles in the ground; thallus thin with perithecia forming shallowly convex to conical projections (graded 2/5),

V.nigrescens, on well-lit calcareous rocks and mortar; looks like darker form of V.macrostoma; described as very common and easily identifiable (graded 1/5),

V.viridula, again very common on calcareous rock in semi-natural habitats, or on bricks and mortar in urban environments; a very variable species, but distinguished by large perithecia (graded 2/5).

Bagliettoa consists of just five species, all previously listed under Verrucaria:

The two most common species are Bagliettoa baldensis and B.parmigera for which there is a separate species account (graded 2/5). The only to consider from this genus locally would be Bagliettoa calciseda, which visually differs by having a white, sometimes flaking thallus, that resembles a coat of white masonry paint (graded 2/5).

Interestingly, as confirmed by the BLS identity grading system, all the species mentioned above are, in theory, recognisable in the field. But, as there are other rarer species that may need to be considered, it's still advisable in most cases to list as 'unidentified' if they haven't been verified.

The final genus Thelidium, includes fourteen species, only four of which are likely to be found locally. They all require microscopic examination, so at best they would only be 'likely'.

T.decipiens, on limestone, calcareous sandstone and mortar,

T.incavatum, occurs on limestone and other calcareous rock; characterised by the relatively large perithecia immersed in pits,

T.papulare, locally common on limestone and calcareous sandstone - often on damp rock; characterised by the relatively large perithecia,

T.zwackhii, seemingly under-recorded, but considered widespread, primarily in woodland, waste ground or beside streams on limestone, chalk and silicious rock; distinguished by small prominent perithecia.

The following are three, presumably different, species that I have not been able to distinguish.