Bacidina species are
crustose lichens, forming thin, often inconspicuous
thalli that may be smooth, cracked, warted, or . Some species develop specialised reproductive structures such as
soredia,
isidia, or microsquamules. The thallus is typically pale in colouration, ranging from whitish and pale green to greyish or fawn. The
photosynthetic partner () consists of algae, which have roughly spherical () to broadly
ellipsoidal cells. The reproductive structures, or
apothecia, are relatively small, usually up to 1 mm in diameter, and can be flat or strongly convex. They lack a distinct but have a well-developed , which is composed largely of thick-walled cells with isodiametric to ellipsoidal . This distinguishes
Bacidina from
Bacidia, which has a true exciple made of radiating
hyphal tissue with narrow lumina. The
hymenium, a spore-producing layer, reacts with
iodine (I+) to
stain blue. The underlying varies in colouration from colourless to pigmented. The
paraphyses within the hymenium are generally few in number, sometimes branched, and often have swollen tips. The
asci, which produce the , are club-shaped () to cylindrical-clavate in shape and typically contain eight spores. Most
Bacidina species have asci of the
Bacidia type, characterised by an apical dome that stains dark blue in K/I with a pale, conical apical cushion. In some species, the ascus resembles the
Biatora type, which has a darker-staining zone around the apical cushion. The ascospores are colourless, generally three- or more-
septate at maturity, and often (thread-like), (needle-shaped), or sigmoid (curved like an "S"), though some species have spores that are cylindrical to fusiform. A distinct outer spore coating () is absent.
Asexual reproduction occurs through
conidia, which are produced in small, often or sessile
pycnidia. The conidia are colourless and vary in shape, with some species producing septate conidia.
Bacidina species do not contain
secondary metabolites that react with common chemical
spot tests (C−, K−, KC−, Pd−, I−, UV−), but their apothecia and pycnidia may contain a variety of pigments. ==Species==