Mazosia is a genus of
crustose lichens, meaning it forms a thin, crust-like layer that adheres tightly to the surface it grows on. The
thallus (lichen body) lacks a protective outer and may sometimes have hair-like extensions on the upper surface. The
photosynthetic partner, or , is typically from the genus
Trentepohlia, with cells that are round to oval (7–17
μm wide) and either occur singly or form short chains. In some cases, the photobiont can be from the genus
Phycopeltis, which has rectangular to rhomboid cells (12–20 by 6–12 μm) arranged in radiating plates. The reproductive structures, called
apothecia, are generally round and have a layered margin, known as a structure. This margin consists of three layers: an inner (the true margin of the apothecia), an outer (derived from the lichen body), and a middle layer of
rhomboid crystals (5–10 μm wide) that do not dissolve when treated with
potassium hydroxide solution (K). The of the apothecia is greyish-black to black and exposed. In cross-section, the proper exciple has a cup-like shape and is made of vertically oriented
hyphae (fungal filaments) that are 3–6 μm thick, red-brown to (blackened) in colour, and turn olive-green when treated with K. The layer beneath the
hymenium, or , is pale brown to colourless. The hymenium (the spore-producing layer) is clear, not filled with oil droplets, and shows a faint blue reaction when treated with
iodine-based stain (
hemiamyloid). The
asci (spore sacs) are cylindrical to club-shaped, usually containing eight spores. They resemble the
vulgata-type asci, where the walls and central structure () are not
amyloid (do not react to iodine), except for a small amyloid ring. The , which are filamentous structures surrounding the asci, are richly branched and connected, often extending well above the height of the asci without swollen or pigmented tips. The ascospores are colourless, elongated (
ellipsoid to spindle-shaped), and divided by 3–7 internal walls (
septate). One central compartment is usually larger than the others.
Mazosia also produces asexual spores in structures called
pycnidia, which can be either embedded within the thallus or slightly protruding. There are two types of asexual spores: larger, oblong to rod-shaped spores (macroconidia) and smaller, spindle-shaped spores (microconidia). Chemically,
Mazosia species typically lack detectable
secondary metabolites (
lichen products), although some species contain the compound
psoromic acid. ==Species==