Niesslia is a genus of small, dark-coloured fungi that typically grow on decaying plant material. These fungi produce distinctive reproductive structures called
perithecia, which are visible to the naked eye as tiny, dark spots on the plant surface. The perithecia of
Niesslia species are key to their identification and exhibit several distinctive characteristics. These tiny, dark reproductive structures are usually round when fresh, but often collapse into a cup-like shape as they dry out. Their outer wall is brittle and typically displays a shiny, blackish-brown colour that catches the eye. A striking feature is the upper part of the perithecium, which is adorned with stiff, dark brown bristles or spines. These spines can vary in complexity, sometimes consisting of just a single cell, while in other cases they are made up of several cells. Occasionally, these spines end in a small, swollen tip known as a vesicle, adding to their unique appearance. Inside the perithecium,
Niesslia deviates from some other fungi by lacking
paraphyses. Instead, the interior houses specialised cells called
asci, which are responsible for producing and containing the fungal spores. The asci in
Niesslia are very thin-walled and can be either cylindrical or club-shaped (clavate). They often narrow at the top and have a flat end. The produced within these asci are colourless and typically have two cells. They can be elliptical, cylindrical, or slightly spindle-shaped.
Niesslia also has an asexual reproductive stage, known as an
anamorph. 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. These asexual spores are typically formed in chains or in slimy clusters. A unique feature of
Niesslia is the presence of characteristic crystals in laboratory cultures. These crystals can have various shapes, including prism-like structures with indented ends, bundle-like formations with ragged ends, or fan-shaped structures. ==Species==