Life habit: lichenized; Thallus: minutely shrubby, ± dichotomously branched, often hemispherical, heteromerous; branches: filamentous, dendroid and often complex, ± terete, with thicker secondary branches towards base and thinner, anastomosing branches at apices; surface: dark, greenish blue to brownish, often shiny towards lobe tips; cortex: well developed, cellular, 1-several cells thick, surrounding a central medullary strand of hyphae; medulla: loosely interwoven, often paraplectenchymatous towards the base; photobiont: primary one a Nostoc or Scytonema, secondary photobiont absent; Ascomata: apothecial, mostly lateral, orange, red-brown or brown, with a sunken disc; exciple: often with pitted, thick-walled cells; paraphyses: unbranched, septate; apices capitate; asci: broadly cylindrical; apices thickened, I+ blue, 8-spored; ascospores: colorless, polymorphic, ellipsoid to spindle-shaped, simple to 1- or 2-septate, thin- or thick-walled; Conidiomata: pycnidial, brown, lateral; conidiogenous cells generally short; conidia: bacilliform; Secondary metabolites: none detected; Geography: North and South America, high altitude areas in tropical E Africa, the Pacific region and Europe; Substrate: on bark or moss.; Notes: The genus is rather distinctive because of its small fruticose growth form with dichotomously branched, terete, corticate lobes. Dwarf fruticose species of Leptogium also have corticate lobes, but these are often wrinkled. Fruticose species of Lichinella lack any cortex and the hymenium is covered by single-celled cyanobacteria and the asci are polyspored and thin-walled. The fruticose species of Peccania possess single-celled cyanobacteria, the lobes lack any cortex, the upper parts of the hymenium is conspicuously reddish-brown colored, the conidia are large and filiform and the asci are thin-walled. In Ephebe and Zahlbrucknerella the fruticose-filamentous thallus lobes are usually adpressed and ecorticate. However, in Zahlbrucknerella there are hyphal strands surrounding the photobiont trichomes. Both, Ephebe and Zahlbrucknerella have thin-walled, often polysporous asci. Thermutis velutina grows on rock and its lobes are smaller and more slender, and its asci are thin-walled. In Spilonema revertens and S. paradoxum the lobes are ecorticate, more irregularly branched and fastened to the substrate by a bluish-black hypothallus.
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