Thallus: fruticose, rigid and shrubby, like rock populations of N. homalea, branching laterally from strap-like blades or unbranched forming smaller cushion-like tufts up to 7 cm long and 4 cm broad branches: flattened or subcylindrical, similar to N. homalea in variability, up to 1.2 cm wide (usually less than 0.5 cm) and 3.5 cm long, surface: yellow-green cortex: rigid, cracking when bent, anatomically the same as N. homalea isidia: coralloid, with blunt tips, unevenly distributed the length of the branches, most common on the terminal half medulla: white, with agglutinated hyphae Apothecia: uncommon, subterminal, up to 7 mm in diam. asci: clavate, 8-spored ascospores: hyaline, 1-septate, fusiform, straight or gently curved, 10-14 x 3-4 µm Pycnidia: black, immersed, same as N. homalea conidia: straight, rod-shaped, 4.5(-6)-1.5 µm Spot tests: negative Secondary metabolites: sekikaic or divaricatic acids, triterpenes, and usnic acid. Substrate and ecology: on rocks World and Sonoran distribution: Channel Islands of southern California, and NW Baja California from San Quintín to central Baja California Sur, including the Vizcaíno Peninsula, Cedros and Guadalupe Islands. Notes: Niebla isidiaescens is a conspicuously coralloid isidiate species clearly derived from N. homalea, which it otherwise resembles. Isidia occur on the lateral and marginal blade surfaces throughout the length of the branches, but are most abundant on the terminal half. Black pycnidia are present on many thalli, but nearly absent on others. Spjut (1996) described the sekikaic race as a species separate from the divaricatic race, however, since we treat divaricatic and sekikaic acid races as one taxon in N. homalea, they are not taxonomically distinguished here either.