Hypoxylon rubiginosum group forms thin, brittle, often extensive purplish crusts on bare, dead wood. There are minute white dots which are the ostioles from which spores emerge. It occurs commonly worldwide and is a group of related species.Hypoxylon rubiginosum group forms thin, brittle, often extensive purplish crusts on bare, dead wood. There are minute white dots which are the ostioles from which spores emerge. It occurs commonly worldwide and is a group of related species. It has been proposed that the name Annulohypoxylon placentiforme should be used for this one. Mortimer Picnic Ground, Bunyip State Forest, 2009.