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Arthonia granitophila Th.Fr.

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Granittflekklav.
Creative Commons Attribution Share-alike | Andreas Frisch

Arthonia granitophila collected from rock at Middagstangjen, Granvin, in Voss (O-L-16563).

Arthonia granitophila is a species of sheltered siliceous rocks. It is known in coastal Norway north to Namsos in Trøndelag. Arthonia granitophila is characterized by rounded to shortly elongated, black apothecia with well-developed margin and exposed disc. The granular thallus contains a trentepohlioid photobiont. The 1-septate spores are brown and warted when old.

Description

Thallus

The thin thallus is dark greenish to yellowish brown. It consists of grey, brownish or rusty orange granules that are best developed around the apothecia. The margin is not determinate. The photobiont is a species of the family Trentepohliaceae.

Fruitbodies

The apothecia are black, rounded to shortly elongate or even shortly branched, and without pruina. They are immersed to raised over the thallus and 0.1–0.4 mm in size. The margin is well-developed and raised over the exposed disc.

The exciple is clearly defined and brown-black in color. It is often extended into a short stipe below the hypothecium.

The epithecium is 5–7 µm tall, dark brown and granular.

The hymenium is colorless to pale brown and 40–50 μm tall.

The hypothecium is dark brown and up to 40 µm tall.

The paraphysoids are ca 1 μm wide and not widened in the tips.

The asci are clavate, 25–45 × 14–20 μm in size and 8-spored.

The spores are colorless first, with a brown pigmentation and granular ornamentation when old. They are obovoid to oblong or slipper-shaped, 10–19 × 3.5–6.5 μm in size, and divided by 1 transverse septum.

Anamorph

The black pycnidia resemble minute apothecia. The wall is dark brown. The oblong conidia are 4–5 × ca 2 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+ blue and KI+ blue.

The dark brown pigment in the exciple, epithecium, and the wall of the pycnidia does not change color in K solution.

Ecology

Arthonia granitophila is a species of shaded siliceous rocks in coastal Norway. It grows in sheltered rock faces and often occurs together with Enterographa zonata, Gyrographa gyrocarpa and Porina lectissima. The species is seldom collected but might be overlooked.

Distribution in Norway and the Nordic countries

Arthonia granitophila is widely distributed in coastal Norway from Oslo in the South to Namsos municipality in Trøndelag. In the Nordic countries, it is further known from Finland and Sweden.

Global distribution

Outside the Nordic Countries, A. granitophila is known from the British Islands and central Europe.

Similar species

Gyrographa gyrocarpa occurs in the same habitat and shares with Arthonia granitophila the black apothecia reminiscent of Opegrapha. It differs from the latter species in the well-developed pale tan to dark chocolate-brown thallus with pinkish soralia and knot-like to gyrose apothecia with slit-like disc. The spores are persistently colorless, larger, 12–30 × 3–6 μm in size, and divided by 3 transverse septa. Gyrophoric and schizopeltic acids are present in G. gyrocarpa (thallus C+ and KC+ red).

Remarks

This species was long included in the unrelated genus Melaspilea, as M. granitophila (Th.Fr.) Coppins. The placement in Arthonia is confirmed by molecular phylogenetic data (Frisch et al. 2014).

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.

Frisch A, Thor G, Ertz D and Grube M (2014). The Arthonialean challenge: restructuring Arthoniaceae. Taxon 63: 727–744.

Wirth V, Hauck M and Schultz M (2013). Die Flechten Deutschlands, vol. 1+2. Ulmer, Stuttgart. 1244s.