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Asci of Morchella elata, Phase contrast image There are eight ascospores in each ascus of Sordaria fimicola. An ascus (from Ancient Greek ἀσκός (askós) 'skin bag, wineskin'; pl.: asci) [1] is the sexual spore-bearing cell produced in ascomycete fungi.
The asci form a layer lacking paraphyses, and they lack croziers. The ascospores frequently bud into multiple yeast cells within the asci. Phylogenetically, Taphrina is a member of a basal group within the Ascomycota, and type genus for the subphylum Taphrinomycotina , the class Taphrinomycetes , and order Taphrinales .
As an ascomycete, Ceratocystis coerulescens produces ascospores encased as groups of eight in asci. The asci are protected by a perithecium, a flask-shaped ascocarp, in which the pathogen overwinters. Ascospores are the sexual spores and are far less common than the asexual spores known as conidia.
The asci typically contain eight spores each. Individual ascospores of Megalospora austropacifica are clear and two-celled, with a slight curve reminiscent of the sulphurata -type spores. They measure 60–85 by 22–26 μm, with spore walls that are 2–3 μm thick and have a thin, smooth outer layer ( epispore ).
The defining feature of this fungal group is the "ascus" (from Ancient Greek ἀσκός (askós) 'sac, wineskin'), a microscopic sexual structure in which nonmotile spores, called ascospores, are formed. However, some species of Ascomycota are asexual and thus do not form asci or ascospores.
The unitunicate asci are usually cylindrical in shape, borne on a stipe (stalk), released from a pore, developed from the inner wall of the perithecium and arise from a basal plectenchyma-centrum. Examples are members of Sphaeriales and Hypocreales .
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The paraphyses are abundant, hyaline (transparent or glass-like), persistent. The asci are 8-spored, unitunicate, pedicellate, persistent, with a J+ or J−, apical ring. Ascospores hyaline, multi-septate, often guttulate, lacking any mucilaginous sheath or appendages. The asexual morph was undetermined (as of March 2021). [10]