[Borrera isidioides (Borrer) Mudd, more]
Thallus: crustose, thin, initiating as isolated verrucae, up to 0.4-0.5 mm wide, developing peripherally to form palmately or radiately isidiate units, up to 0.8-1 mm wide surface: light gray, dull; margin: indeterminate; prothallus: lacking isidia: coralloid, dichotomously branched or not, up to 0.3-0.4 mm long, c. 0.1 mm wide Apothecia: sessile, scattered, up to 0.8-1 mm in diam. disc: brown, becoming dark brown to blackish brown, concave becoming plane thalline margin: concolorous with thallus, entire or crenulate, c. 0.1 mm wide, or developing isidia; excipular ring: absent thalline exciple: 70-110 Ám wide laterally; cortex: 10-40 Ám wide; cells: up to 4-4.5 Ám wide, not pigmented; algal cells: 9-13 Ám in diam.; thalline exciple: 60-140 Ám wide below; cortex: expanded, 25-60 Ám thick, also cellular proper exciple: hyaline, 10-15 Ám wide laterally, extending beneath hypothecium, up to 30-35 Ám at periphery hymenium: 120-130 Ám tall; paraphyses: 2-3 Ám wide, conglutinate, with apical cells to 3-4 Ám wide, not or lightly pigmented, forming a very light orange-brown epihymenium; hypothecium: hyaline, 70-80 Ám thick asci: clavate, 90-120 x 25-30 Ám, 4-8-spored ascospores: brown, 1-septate, ellipsoid, type A development, Pachysporaria-type, (24-)28.5-30.5(-34.5) x (11.5-)14.5-15.5(-18.5) Ám, transient polygonal lumina early in development, becoming irregularly rounded with small, apical lumina differentiating in some mature and overmature spores, often slightly waisted at maturity; torus: narrow; walls: not ornamented Pycnidia: not seen Spot tests: K+ yellow, C-, KC-, P+ faint yellow Secondary metabolites: atranorin in cortex, zeorin (minor) in medulla. Substrate and ecology: on bark, especially on Quercus, sometimes over mosses World distribution: an extreme oceanic species of western Europe (southwestern Norway to Portugal) Sonoran distribution: Chihuahua, localized in the Sierra Madre Occidental. Notes: An easily recognized species characterized by its large, often branching isidia, cortical atranorin, and large Pachysporaria-type spores developing ancillary, apical lumina. Other species with spores possessing apical lumina are the saxicolous R. verruciformis, also with a Sierra Madre distribution, and R. confinis Samp., another extreme oceanic European species with a distribution similar to R. isidioides and with which it sometimes occurs. It is a new record for North America.