Genus Bathelium features a corticate thallus (a protective outer layer) usually with olive-green to brownish or greyish hues. This genus is distinguished by the form of its ascomata, the spore-producing structures, which possess apical ostioles (openings at the top). These ascomata can be found either singly or in groups, and often form pseudostromata, a stroma made of both thallus tissue and bits of host tissue. They are noticeable, ranging from prominent to sessile, and show a brown-black colouration, though in rare instances, they may have a whitish pruinose (powdery) appearance. This is complemented by a peripheral layer made up of tightly packed cells.[3]
Within the ascomata, the hamathecium, a tissue layer containing filamentous structures, is clear and hyaline (translucent). It comprises thin, interconnecting filaments known as paraphysoids. The ascospores number from one to eight per ascus. They are transversely septate to muriform (divided into compartments by cross walls), with thin septa and more or less angular lumina. These spores are fusiform, meaning they have a spindle-like shape, with either acute (pointed) or rounded ends, and are not constricted at the median septum. They appear hyaline, do not react to iodine (IKI−), and are encased in a gelatinous sheath.[3]
No conidiomata (structures responsible for asexual reproduction) have been identified in this genus. In terms of chemical properties, Bathelium frequently contains anthraquinones, compounds often present internally in pseudostromata. Lichexanthone, a fluorescent xanthone compound, is occasionally found within the genus.[3]
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