The Bionectriaceae are a diverse family of ascomycete fungi in the order Hypocreales, best known for their small, often vividly coloured fruiting bodies and their wide range of ecological roles. Members of this family may be saprobic, fungicolous (growing on other fungi), or weakly parasitic on lichens, slime moulds, or other microfungi. Although usually inconspicuous, they can be recognised by their minute, soft perithecia, often in shades of yellow, orange, red, or white, and by their thin-walled, hyaline ascospores.

Nectriopsis is a genus of tiny, soft-textured perithecial ascomycetes in the Bionectriaceae, best known for growing directly on other fungi, especially corticioid crusts, polypores, and occasionally lichenised fungi. Species typically form clusters of minute, brightly coloured perithecia, often orange, red, or yellow, that stand out sharply against the substrate. Because of their small size (usually <0.5 mm), they are easily overlooked unless the host fungus is examined closely.