Scytinium is a genus of lichen-forming fungi in the family Collemataceae. It has 49 species. These lichens are typically found on basic rocks, soil, and trees, occasionally in association with mosses. Despite the morphological and ecological diversity within Scytinium, its species share similar features, such as shape and septation, as well as a small to medium-sized thallus with at least a partial .
Scytinium encompasses lichen species that exhibit a variety of thallus forms, such as crustose, squamulose,, or . These lichens have a gelatinous texture, and their colour ranges from dark brown and bluish-grey to olive-green. The of Scytinium can be spreading, elongate, or somewhat cylindrical in shape. The upper and lower, when present, is composed of either cuboid cells or flattened, degraded tissue. The medulla contains loosely interwoven or compact hyphae, along with the photobiont Nostoc–a common genus of cyanobacteria.Both the upper and lower surfaces of Scytinium lichens can vary from smooth to wrinkled or ridged and typically exhibit a matte appearance. While isidia may or may not be present, soredia are absent in this genus. The cells are generally arranged in distinct chains. The ascomata are in the form of apothecia with a red-brown, which can be sessile, laminal, or marginal. The is smooth to, to, and often persistent. The is raised, cup-shaped, and predominantly composed of cells, ranging in colour from colourless to reddish-brown. The disc is either concave or flat.
The is colourless to reddish-brown and does not react with a solution of potassium hydroxide or ammonia. The hymenium is colourless, turning blue when exposed to iodine. The is shallow, and its colour varies from colourless to pale yellowish. The consists of numerous, that separate in potassium hydroxide and sometimes have branched apices that are somewhat swollen. The asci contain eight spores and are club-shaped (clavate), with a strongly thickened apex that reacts to potassium hydroxide and iodine, turning blue. are primarily ellipsoidal,, and colourless, lacking any distinct surface ornamentation or ., or, are infrequent in cytinium species. No lichen products have been detected in Scytinium species using thin-layer chromatography.
, Species Fungorum (in the Catalogue of Life) accepts 47 species of Scytinium.