Microthecium produces small, nearly spherical perithecia (fruiting bodies) that may be superficial or partly immersed in the substrate. Unlike the closely related Melanospora, the perithecia in Microthecium lack an ostiole (a visible opening), and also lack the specialised hairs that often surround the ostiole in ostiolate relatives. The perithecial wall is pale (yellow to light yellowish brown) and membranaceous, often appearing darker as the spore mass develops. The asci are typically eight-spored but short-lived, breaking down at maturity so the ascospores accumulate as a dark mass in the cavity. The ascospores are single-celled and dark-coloured at maturity, commonly lemon-shaped (though sometimes ellipsoid or fusiform), and their walls range from smooth to distinctly reticulate (net-like) depending on species. When present, the asexual stage consists of phialides producing small, hyaline (colourless) phialospores, and chlamydospores may also occur. Species of Microthecium are usually parasitic or commensal on other fungi, but some have been recovered from soil.[2]
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