Life habit: lichen-forming Thallus: white to pale gray, rarely pale red, sometimes with greenish tinge, effuse, often disrupting bark tissue, ±smooth, often bordered by red-brown prothalline lines; thallus in section up to 70 µm thick photobiont: Trentepohlia; cells: globose to ellipsoid, 8-15 x 4-12 µm, in short chains Ascomata: scattered to crowded, developed in outermost bark layers, soon erumpent and sessile, ±round, not distinctly branched, 0.12-0.5 mm wide, in section 100-150 µm thick disc: below the pruina fox-brown to almost hyaline, flat to convex, often densely covered by reddish or white pruina (if with white pruinose, then reddish pruina restricted to the periphery); below the ascomatal flanks often with dark violaceous, non-crystallized pigment; peripheric hyphal structures: composed of well differenciated, branched and anastomosing hyphae, with cells: 5-7 x 2-4 µm, with chestnut brown tinged outer cell walls; often incrusted by orange red grains epihymenium: ±interspersed with orange red grains and/or hyaline rhombic crystals, 10-20 µm thick; hyphae anastomosing and especially in outer parts branched and interlocking, outer cell walls hyaline (occasionally, when densely pruinose) to brown (often or when pruina reduced); cells 4-6 x 1.5-2 µm hymenium: hyaline to pale yellow, 60-100 µm tall, with closely spaced asci; paraphysoids: well developed and distinct in young ascomata, occasionally collapsed in mature ascomata, branched and anastomosing (especially above the asci), hyphae slightly sinuouse, irregularly thick; cells: 3-8 x 0.5-1 µm; subhymenium: hyaline to yellowish or pale reddish brown, 25-50 µm thick; cells irregularly ±round, 2-5 µm in diam., often without plasmatic content and ±collapsed; pigments amorphous, in and between the cell walls asci: clavate to broadly clavate, 60-80 x 20-25 µm, lateral walls ±thin, base not very distinct, 8-spored ascospores: initially hyaline but becoming externally brown, 4-7 septate (not incised at the septa), septation proceeding from the upper third downwards, oblong ovoid, 20-33 x 5.5-11 µm Pycnidia: very rare, ±round, 110-130 µm in diam. conidia: hyaline, non-septate, bacilliform, 4-6 x 1-1.5 µm Chemical reactions: ascomatal gels I+ blue; walls of thallus hyphae I+ pale blue; ascomatal gels KI+ blue; reddish pigments of epihymenium K+ red violet and dissolving; asci without KI+ blue tholus structures. Substrate and ecology: on bark of various trees, mainly on smooth substrates World distribution: widely distributed in tropical and temperate regions, including Europe and North America Californian distribution: north central California (Mendocino Co., Fort Bragg) Notes: Arthonia cinnabarina is extremely variable in morphology and anatomy throughout its geographic range. It is likely that this phenotypically circumscribed species is composed of several biologically separate lineages. The presence of genetic differences is assumed due to slight, yet consistent differences in shapes of fully developed ascomata within geographically limited morphotypes. These differences do not suffice to split microspecies in this complex, primarily because considerable variation of ascomatal morphology within thalli will make it difficult to recognize such taxa unambiguously. In TLC analyses, this species displays up to 5 different reddish pigments in their ascomata (Grube unpublished). Pigments produced by a mycobiont culture of A cinnabarina were identified as the aza-anthraquinone bostrycoidin (known from Fusarium) and the isofuranonaphthoquinone arthoniafurone A & B (minor novel yellow pigments) (Yamamoto et al. 2002). The species is documented north of the Sonoran region but is also expected to occur further south. Closely related taxa are A. redingeri and A. speciosa, which can be distiguished by their spores size and type of septation, as well as by their ascomatal shape and pigmentation. A further subtropical species occurring in North America is A. rubrocinta G. Merr nom. nud., known from Florida, and apparently confined to Sabal palmetto as a substrate. This species differs by its rather narrow ascospores (18-23 x 5-6 µm) and the presence of psoromic acid in the thallus.