The
thallus (the main lichen body) of
Toninia is often reduced or even absent; when present it is usually , meaning it is made up of small, scale-like pieces that can proliferate and merge into an almost continuous crust. In some species the surface becomes nodular or . The upper (the protective skin) ranges from poorly to well developed and may carry a thin (a film of dead, compacted cells); it lacks surface crystals and shows no fissures or
pseudocyphellae (tiny breaks in the cortex that look like pores). A lower cortex is weak or missing. The
green-algal partner is ; that is, it consists of simple, spherical green cells, arranged either in a continuous band beneath the cortex or in scattered patches. The
medulla (internal white tissue) typically lacks crystals.
Fruiting bodies are
apothecia (open discs) that are black and not (they do not carry a pale, dusty bloom). They are usually flat when young but commonly become convex with age. A (a rim made from the thallus) is lacking. Instead, the apothecium has a (a structural rim of fungal tissue) that is initially raised and clear-cut but is often overgrown and excluded later. Microscopically, this exciple is built from radiating, thick-walled, glue-bound
hyphae whose cell cavities are rounded to narrowly cylindrical; the inner part is colourless, while the outer edge is dark brown (sometimes with a greenish cast). These tissues lack crystals and have characteristic reactions to standard chemical
spot tests: K (
potassium hydroxide) negative; N (
nitric acid) negative or, more typically, N+ (violet) owing to a pigment sometimes termed "Bagliettoana-green". The (the film over the spore-bearing layer) is usually olive to green, rarely brown or colourless, also without crystals, K– and usually N+ violet. The
hymenium (spore-bearing layer) turns I+ (blue) with iodine, whereas the (the tissue below) is colourless to dark brown and contains no crystals. The consists of straight
paraphyses (sterile threads) that are unbranched or only sparsely branched and sometimes interlinked; they are not cemented together and have thin walls, with the tip cell distinctly swollen and capped by a gelatinous pigment dome. The
asci are of the
Bacidia-type: club-shaped, eight-spored, and sheathed in a gelatinous wall that becomes K/I+ blue (a potassium hydroxide pre-treatment followed by iodine). Each ascus has a well-developed, iodine-positive with a darker-staining central tube and a pronounced (a clear area at the apex involved in spore release).
Ascospores are colourless and smooth, ranging from non-
septate to 7-septate; shapes vary from
ellipsoidal to narrowly spindle-shaped () or needle-like ().
Asexual structures (
conidiomata) are
pycnidia that appear black and are immersed to slightly protruding; they produce
conidia that are rod-shaped to thread-like. In terms of chemistry, the genus is generally poor in distinctive
secondary metabolites: at least one species has been reported with
terpenoids, and there are occasional reports of
stictic acid and/or
xanthones in two taxa that likely do not belong in
Toninia and may require exclusion. ==Species==