Arthonia caesiella Nyl.

Bot. Not.: 161, 1853.
Synonyms: Arthonia aphthoides Flagey nom. superfl.; Arthonia aphthosa Flagey; Arthonia galactiformis Flagey
Distribution: C - Sar (Sundin 1999).
Description: Thallus crustose, endosubstratic or thinly episubstratic, poorly delimited, pale grey to white. Apothecia arthonioid, emarginate, half-immersed to adnate, round to elongate and then simple with rounded ends, up to 1 mm long and up to 0.25 mm wide, black but usually blue-grey-pruinose. Proper exciple not developed; epithecium blackish, overlain with crystals (pruina), c. 15 μm high, K+ greenish: hymenium colourless to pale yellow, 30-50 μm high, I+ blue; paraphysoids coherent, thread-like, the apical cells hardly swollen: hypothecium pale ochraceous yellow, poorly delimited from hymenium, c. 20 μm high. Asci 8-spored, broadly clavate to subglobose, semi-fissitunicate, with a large apical dome, a distinct ocular chamber, and a K/I+ bluish ring-structure, Arthonia-type. Ascospores 1-septate, with unequal cells, hyaline, ovoid, rounded at one end, pointed at the other, 12-16 x 6-7 μm. Photobiont: trentepohlioid. Spot tests: thallus K+ pale yellow, C-, KC-, P-. Chemistry: unknown.
Note: a Mediterranean-Atlantic species found on smooth bark of deciduous and coniferous trees. Perhaps more widespread in the humid parts of Mediterranean Italy. 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
Pioneer species

Commonnes-rarity: (info)

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


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Harrie Sipman
Karpathos (Sipman & Raus 56349)
Identification not certain