Arthonia medusula (Pers.) Nyl.

Mém. Soc. Imp. Sc. Nat. Cherbourg, 5: 132, 1857. Basionym: Opegrapha medusula Pers. - Ann. Wetter. Gesellsch. Ges. Naturk., 2: 15, 1810.
Synonyms:
Distribution: N - Ven. C - Laz.
Description: Thallus crustose, episubstratic, thin, whitish to yellowish white. Apothecia arthonioid, lirelliform, brown-black, semi-immersed in the thallus, 0.5-2 mm long, branched to stellate, with a mostly flat, grey-pruinose or rarely epruinose disc. Epithecium blue-black, rarely dark olive-brown, K+ greenish; hymenium colourless to pale brown, 50-75 µm high, I+ blue; hypothecium colourless to pale yellowish. Asci 8-spored, broadly clavate, semi-fissitunicate, with a large apical dome and a distinct ocular chamber, Arthonia-type. Ascospores (2-)2-3(-4) septate, hyaline, more or less fusiform, 9-18 x 2-3 µm, the apical cell not enlarged. Pycnidia common, black but often white-pruinose, slightly emerging from thallus. Conidia bacilliform, 5-6 µm long. Photobiont trentepohlioid. Spot tests: thallus K- or K+ yellowish, C-, KC-, P-. Chemistry: unidentified substances in thallus.
Note: a mild-temperate, suboceanic lichen found on old oaks, in dry parts of the trunks seldom wetted by rain, in parklands and open woodlands. The record from Veneto (see Nimis 1993: 80) requires confirmation. The species is included in the Italian red list of epiphytic lichens as “Critically Endangered” (Nascimbene & al. 2013c).
Growth form: Crustose
Substrata: bark
Photobiont: Trentepohlia
Reproductive strategy: mainly sexual
Most common in areas with a humid-warm climate (e.g. most of Tyrrenian Italy)
In underhangs rarely wetted by rain

Commonnes-rarity: (info)

Alpine belt: absent
Subalpine belt: absent
Oromediterranean belt: absent
Montane belt: absent
Submediterranean belt: extremely rare
Padanian area: absent
Humid submediterranean belt: extremely rare
Humid mediterranean belt: absent
Dry mediterranean belt: absent


pH of the substrata:

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5

Solar irradiation:

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Aridity:

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Eutrophication:

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Poleotolerance:

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Altitudinal distribution:

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P.L. Nimis; Owner: Department of Life Sciences, University of Trieste
Herbarium: TSB (5733)
2003/01/23



Elena Pittao; Owner: Department of Life Sciences, University of Trieste
Herbarium: TSB 5733



Elena Pittao; Owner: Department of Life Sciences, University of Trieste
Herbarium: TSB 5733


Redinger, K. (1938) Arthoniaceae, Graphidaceae . In Kryptogamen-Flora von Deutschland, Österreich und der Schweiz. Band 9, 2 Abt., Part 1 (G. L. Rabenhorst, ed.): 181–404. Leipzig: Borntraeger