Mariannaea is a genus of fungi belonging to the family Nectriaceae.

[2] The genus is characterized by branched, septate conidiophores with hyaline, flask-shaped phialides, 1–2-celled hyaline conidia mostly forming imbricate chains or slimy heads (Samson 1974;[2] Samson and Bigg 1988;[3] Samuels and Seifert 1991).

[4] The sexual morph of Mariannaea has been linked to genus Nectria (Samuels and Seifert 1991),[4] and genus Cosmospora (Gräfenhan et al.

[5] However, Cosmospora and Nectria have been shown polyphyletic within the Nectriaceae family, while genus Mariannaea formed a monophyletic clade within Nectriaceae.

Therefore, Gräfenhan et al. (2011) retained Mariannaea as a distinct genus in Nectriaceae.