ostiolum

Noun

ostiole (plural ostioles)

1. A small hole or opening through which certain fungi release their mature spores.
   • The Erysiphacae may possibly have given rise to the Laboulbeniales, the only other group in which a single daughter cell of the oogonium is responsible for the asci, and perhaps to the lower Pyrenomycetes also; these, like the Erysiphaceae, have regularly arranged asci, and in Chaetomium fimete the...2010, Helen Gwynne-Vaughan, Fungi: Ascomycetes, Ustilaginales, Uredinales, page 54
2. A similar hole or opening in plants, such as the opening of the involuted fig inflorescence through which fig wasps enter to pollinate and breed.