Asteristion

Asteristion is a genus of lichen-forming fungi in the family Graphidaceae. It has seven species. Previously considered a synonym of either Phaeotrema or Thelotrema, molecular evidence led to its resurrection as a distinct genus. Asteristion lichens are corticolous (bark-dwelling), featuring a continuous thallus with a loose to hardened cortex and a photobiont layer containing calcium oxalate crystals. The ascomata, or fruiting bodies, are characterized by their large, often chroodiscoid appearance and the presence of distinct periphysoids. The secondary chemistry of these lichens includes major concentrations of stictic acid and minor to trace amounts of associated substances....read more on Wikipedia.