Thallus: immersed, or thin, continuous; prothallus: not apparent surface: gray to bluish white, smooth; photobiont: chlorococcoid, cells +spherical, up to 25 µm in diam. Apothecia: scattered to clustered, evenly distributed (not crowded), sessile or constricted at base, orbicular at first, peltate, 0.6-1.6 mm in diam. disc: orange-brown, red-brown to lead brown or brown to almost black, smooth, plane initially but becoming concave and sinuous, epruinose or slightly pruinose margin: white, persistent, entire, even or flexuose, continuous, sometimes becoming raised above the disc and involute when old, thin +0.05 mm thick amphithecium: present, with algae in the medulla but not abundant, corticated; cortex: distinctly delimited, gelatinous, thin laterally (30-40 µm), and expanded at the base (up to 70-80 µm), some granules at the top of margin present (pol+, insoluble in K, soluble in N) parathecium: indistinct epihymenium: yellow-brown or pale red, not at all granular, N+ pale red hymenium: hyaline, 45-60 µm tall; paraphyses: coherent, compact, 1-1.5 µm thick below, septate, simple to sparsely branched, expanded at top, brown to red pigmented, tips up to 3 µm in diam.; subhymenium: hyaline, indistinct; hypothecium: hyaline, distinct, up to 80 µm thick asci: clavate, 33-45 x 10-15 µm, 8-spored, with biseriate spores ascospores: hyaline, simple, ellipsoid to oval, 8.9-13.3 x 5.0-5.9 µm Pycnidia: not observed Spot tests: apothecia K-, C-, KC-, P- Secondary metabolites: none detected. Substrate and ecology: on the eelgrass Zostera, detritus, wood or tree branches World distribution: arctic-boreal in Europe, northern parts of North America, usually coastal (but also found in Alberta according to Thomson 1997), up to 200 m Sonoran distribution: southern California (San Miguel Island). Notes: Lecanora zosterae is morphologically and chemically uniform. It is a member of the L. dispersa group, and is recognized by its characteristic large, plane to peltate apothecia, with brown or, more usually, deep brown epruinose discs which become wavy and concave when old, with persistent white or whitish gray thin margins.