Arthonia cretacea Zahlbr.

Österr. bot. Z., 68: 148, 1919.
Distribution: S - Si (Nimis & al. 1994).
Description: Thallus crustose, episubstratic, 1-1.5 mm thick, ecorticate, forming chalky white, smooth or undulate, well-delimited, up to 2-(-3) cm wide, often confluent patches, without a distinct prothallus. Apothecia arthonioid, black but often grey-pruinose, rounded to elongate, 0.7-1.5 mm across, at first immersed, then broadly sessile, flat to finally convex, without a distinct margin. Proper exciple poorly developed; epithecium green-black, 20-25 μm high; hymenium colourless to very pale brown, 50-85 μm high, I+ blue; paraphysoids thread-like, branched and anastomosing in upper part, with thicker apical cells; hypothecium well-developed, brown-black, wedge-shaped and paler brown in lower part. Asci 8-spored, broadly clavate, semi-fissitunicate, with a large apical dome, a distinct ocular chamber, and a K/I+ bluish ring-structure, Arthonia-type. Ascospores 3-septate, at first hyaline, but turning brown when overmature, with 4 unequal loculi, spindle-shaped, straight, with rounded ends, 10-13 x 5-6 μm. Pycnidia semi-immersed, black, somehow shiny. Conidia bacilliform, straight, 6-8 x c. 1 μm. Photobiont trentepohlioid. Spot tests: thallus K-, C-, KC-, P-, UV-. Chemistry: without lichen substances.
Note: a mainly Mediterranean species found in shaded, rain-protected surfaces of calcareous rocks subject to humid maritime winds.
Growth form: Crustose
Substrata: rocks
Photobiont: Trentepohlia
Reproductive strategy: mainly sexual
In underhangs rarely wetted by rain
Taxon bound to maritime-coastal situations

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

pH of the substrata:


Solar irradiation:








Altitudinal distribution:


Predictive model
Herbarium samples

P.L. Nimis; Owner: Department of Life Sciences, University of Trieste
Herbarium: TSB (16495)

P.L. Nimis; Owner: Department of Life Sciences, University of Trieste
Herbarium: TSB (16495)

Domenico Puntillo; Owner: Domenico Puntillo

Domenico Puntillo; Owner: Domenico Puntillo

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