Heppia lutosa

Heppia lutosa has a squamulose (scaly) thallus made up of small, leaf-like lobes that are rounded to irregularly lobed and measure up to about 10 mm across. The squamules are attached to the substrate by a central umbilicus and range from flat or slightly wavy to distinctly convex, with margins that typically curve downwards. The upper surface is smooth and dark olive in colour, underlain by a thin surface layer. The underside is also smooth, and varies from pale flesh-brown to deep reddish or almost blackish brown; its cortex is formed of paraplectenchymatous tissue that may appear palisade-like and is about 10–50 (sometimes up to 75) micrometres thick. The medulla is differentiated into an upper zone containing the photobiont, which occupies about one-quarter to three-quarters of the medullary depth, and a lower zone of loose, algae-free fungal hyphae.^[5]

Asexual reproduction occurs through soredia, which are produced in usually well-defined soralia situated either along the margins or across the surfaces of the squamules. Sexual fruiting bodies (apothecia) are commonly numerous on each squamule; they are immersed in the thallus so that only the disc is visible at the surface, ranging from punctiform (point-like) to about 0.7 mm in diameter. The ascospores are ellipsoid and relatively small, measuring about 6–8 by 3–5 μm.^[5]

Heppia lutosa has been documented from Africa, Europe, and North America.^[5]