These organisms, which are barely visible to the naked eye, are found in decaying plant matter and are parasites of lichens, other fungi, or nematode eggs.

They belong to the ascomycetes and in their teleomorphic (sexual) stage they form distinctive dark brown shiny fruiting bodies with spines.

These fungi produce distinctive reproductive structures called perithecia, which are visible to the naked eye as tiny, dark spots on the plant surface.

In this stage, the fungus produces structures called phialides, which are specialised cells that generate asexual spores (conidia).

The phialides in Niesslia have a distinctive shape, often with a thickened wall in the lower part and a narrow, thin-walled neck at the top where spores are produced.