Arthothelium norvegicum
Arthothelium norvegicum collected from dead twigs of Picea abies in a boreal rainforest at Engan N in Overhalla (O-L-186266).
Arthothelium norvegicum is confined to the boreal rainforests in Trøndelag and Nordland. It is characterized by the brownish black, rounded to elliptical, moderately convex apothecia on a thin pale thallus with trentepohlioid photobiont. The colorless spores are divided by 7–9(–10) transverse and 2–3 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, pale green grey, immersed in the bark substrate, and has a smooth, matt to weakly glossy surface. 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 raised above the thallus, rounded to elliptical in shape, brownish black, and without pruinado. They are 0.3–0.6 in size and 90–130 μm tall. The disc is slightly to moderately convex.
The epithecium is 7–15 μm tall, reddish brown.
The hymenium is colorless or pale brown and 70–100 μm tall.
The hypothecium is unpigmented or reddish brown in patches and up to 30 μm tall.
The paraphysoids are 0.7–1.5 μm wide. Their tips are widened to 2.5 µm, free and with brown pigment deposited on the outer walls which occasionally form distinct caps.
The asci are of the Arthonia-type, broad obovoid, and 8-spored.
The spores are colorless first, turning brown with granular ornamentation when old. They are oblong to obovoid, 30–42(–49) × 12–16 μm in size, and divided by 7–9(–10) transverse septa and 2–3 longitudinal septa. An enlarged and undivided end cell is not developed.
Anamorph
Pycnidia are unknown.
Chemistry
The thallus does not react with C, K, KC, Pd, or UV (C–, K–, KC–, Pd–, UV–). Lichen secondary compounds are not detected by TLC.
The hymenium reacts I– and KI+ pale blue. A KI+ blue ring structure is present in the tholus of the asci.
The brown pigment in the epithecium changes to greenish in K solution.
Arthothelium norvegicum collected from the base of Sorbus aucuparia at Gårdsetervatnet Ø in Namsos (O-L-221929).
Ecology
Arthothelium norvegicum is a highly oceanic species that is known in Norway from the boreal rainforests in Trøndelag and Nordland. It typically occurs on the smooth bark of rowan (Sorbus aucuparia) and other deciduous trees, but is also found on thin, living twigs of Norway spruce (Picea abies).
The species is additionally reported from common heather (Calluna vulgaris) in coastal heath in the British Islands, and from the slightly shaded to well-lit smooth bark of angiosperm shrubs and trees growing along riparian corridors in wet, low-elevation, coastal habitats in western North America.
Distribution in Norway and the Nordic countries
Arthothelium norvegicum is known from Ørland and Indre Fosen municipalities in Trøndelag to Brønnøy municipality in Nordland. The species is mainly coastal in distribution, with few localities further inland near Stjørdal, Snåsavatnet and along the Namsen valley. A single occurrence has been reported from Åsele lappmark in Sweden.
Global distribution
Outside the Nordic Countries, A. norvegicum is known from highly oceanic, coastal habitats in Western Scotland, Western Ireland, Madeira, and the Pacific coast from northern California to British Columbia (Canada) in North America.
Arthothelium norvegicum collected from an old Sorbus aucuparia at Storsteinbekken N in Namsos (O-L-186348).
Similar Species
Arthothelium norvegicum cannot easily be mistaken for any other Arthothelium species in Norway. Arthothelium ruanum, which can grow in the same habitat, can be separated by the smaller ascospores, 15–26 × 7–10 μm in size. The apothecia of A. ruanum often disintegrate in the centre and regenerate into characteristic aggregations of individual apothecia.
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.
Coppins BJ and Tønsberg T (1984). A new species of Arthothelium from Norway. Nordic Journal of Botany 4: 75–77.
Holien H (1992). Some lichen species new to Norway and Sweden. Graphis Scripta 4: 69–71.
Tønsberg T and Williams C (2006). Arthothelium norvegicum in North America. Evansia 23: 80–81.