Scytinium
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 .

Description
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 isodiametric 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
, Species Fungorum (in the Catalogue of Life) accepts 47 species of Scytinium.

Scytinium apalachense 
Scytinium aquale 
Scytinium aragonii 
Scytinium biatorinum 
Scytinium bosoense 
Scytinium californicum 
Scytinium callopismum 
Scytinium cellulosum 
Scytinium chibaense 
Scytinium contortum 
Scytinium dactylinum 
Scytinium erectum 
Scytinium euthallinum 
Scytinium ferax 
Scytinium fragile 
Scytinium fragrans 
Scytinium gelatinosum 
Scytinium imbricatum 
Scytinium intermedium 
Scytinium juniperinum 
Scytinium kauaiense 
Scytinium leptogioides 
Scytinium lichenoides 
Scytinium magnussonii 
Scytinium massiliense 
Scytinium palmatum 
Scytinium palustre 
Scytinium parculum 
Scytinium parvum 
Scytinium platynum 
Scytinium plicatile 
Scytinium polycarpum 
Scytinium pulvinatum 
Scytinium quadrifidum 
Scytinium rivale 
Scytinium rogersii 
Scytinium schraderi 
Scytinium singulare 
Scytinium siskiyouense 
Scytinium subaridum 
Scytinium subfragrans 
Scytinium subtile 
Scytinium subtorulosum 
Scytinium tacomae 
Scytinium tenuilobum  – Australia
Scytinium tenuissimum 
Scytinium tetrasporum 
Scytinium turgidum

References

Peltigerales
Taxa described in 1810
Taxa named by Erik Acharius
Peltigerales genera
Lichen genera