Arthothelium ruanum
Arthothelium ruanum is a southern species of humid forests and woodlands. It is characterized by black maculate apothecia that often disintegrate in the centre and regenerate into swarms of minute juvenile apothecia. The photobiont is trentepohlioid. The brown and warted spores are divided by 5–8 transverse and 1–3 longitudinal septa. The apical cell is not enlarged.
- Innhold
- Description
- Ecology
- Distribution in Norway and the Nordic countries
- Global distribution
- Similar species
Description
Thallus
The thallus is thin, continuous to cracked, and pale grey, pale olive-grey or brownish grey. The margin is not determinate or bordered by a thin brown line. The photobiont is a species of the family Trentepohliaceae.
Fruitbodies
The apothecia are either level with the thallus surface or indistinctly raised. They are rounded, angular or lobed, brownish black, and do not have pruina. They are 0.4–1.6(–2) mm in size and 70–110 μm tall. The apothecia regularly disintegrate in the centre and regenerate into aggregations of individual apothecia that are characteristic for the species.
The epithecium is 10–15 μm tall, dark reddish brown, with pigment granules.
The hymenium is colorless to pale reddish brown and 35–60 μm tall.
The hypothecium is dark reddish brown and up to 30 μm tall.
The paraphysoids are 1–1.5 μm wide. Their tips are slightly widened to 2–3 µm, free, and lack distinct apical caps.
The asci are clavate, 33–60 × 15–26 µm in size, and 8-spored.
The spores are colorless at first and turn brown with granular ornamentation when old. They are narrowly obovoid, 15–26 × 7–10 μm in size, and divided by 5–8 transverse septa and 1–3 longitudinal septa. An enlarged and undivided apical cell is not developed.
Anamorph
Pycnidia are brownish black, are either immersed in the thallus or slightly raised, and 60–100 µm in size. The wall is reddish brown. The rod-like conidia are 4–6 × 0.8–1 μm in size.
Chemistry
The thallus does not react with C, K, KC, Pd, or UV (C–, K–, KC–, Pd–, UV–). Lichen secondary compounds have not been detected by TLC.
The hymenium reacts I+ red and KI+ deep blue. A KI+ blue ring structure has been observed in the asci.
The brown pigment in the epithecium and in the wall of the pycnidia changes to greenish in K solution.
Ecology
Arthothelium ruanum grows on the smooth bark of deciduous trees, frequently on alder (Alnus spp.), common hazel (Corylus avellana), European ash (Fraxinus excelsior), oak (Quercus spp.), and rowan (Sorbus excelsior). It typically occurs in shady forests and woodlands with a humid microclimate, often along streams or lake shores, swamps and mires. The species is often found towards the base of the trees.
Arthothelium ruanum is a temperate species that in Europe is absent from northern Fennoscandia as well as from a true Mediterranean climate.
Distribution in Norway and the Nordic countries
Arthothelium ruanum is a southern species in Norway. Its known distribution extends to Steinkjer in Trøndelag, with a large gap in the mountains of central Norway. In the Nordic countries, it is also known from Denmark, Finland and Sweden.
Global distribution
Outside the Nordic Countries, Arthothelium ruanum is widely distributed in temperate Europe, N. America and Asia.
Similar species
The characteristic aggregations of regenerating apothecia make A. ruanum a distinct species that, when well-developed, cannot be mistaken for any other Arthothelium species in Norway.
Literature
Cannon P, Ertz D, Frisch A, Aptroot A, Chambers S, Coppins BJ, Sanderson N, Simkin J and Wolseley P (2020). Arthoniales: Arthoniaceae. Revisions of British and Irish Lichens 1: 1–48.
Sundin R (1999). Phylogenetic and taxonomic studies within Arthonia Ach. (Ascomycetes, Arthoniales). Doctoral dissertation, Department of Bot., Stockholm University.