Subhymenium
subhymenium (noun, pl. subhymenia;ascocarp term; synonym: lower thecium) – the layer of ascogeneous hyphae directly below the hymenium. The term is sometimes used in a broad sense as an equivalent of hypothecium even though it is strictly not part of this layer. The ascogeneous hyphae forming the subhymenium do not belong to hyphae that form the surrounding wall of a primordium. Instead they are directly derived from the primordium itself. In some treatments the terms subhymenium and hypothecium have unfortunately been reversed, thus hypothecium has sometimes been used to refer to the ascogeneous hyphae and subhymenium has been used to refer to the lower part of the proper exciple. Using these terms in this reversed order does not make sense, because the term subhymenium implies a layer directly below the hymenium, whereas the term hypothecium implies a layer below the thecium. Thus, a hypothecium is a layer below hymenium and ascogeneous hyphae, i. e., the hyphae from which asci grow into the hymenium. One possible reason, why subhymenium and hypothecium are sometimes used as synonyms or even in a reversed order is the poor differentiation of these hyphal layers in the majority of ascocarps. Only in few species are the two separate layers distinctly differentiated by colour or structure. In the majority of ascomycetes the subhymenium is simply a thin layer of irregular hyphae immediately below the hymenium that are rarely pigmented, whereas a hypothecium is usually more strongly developed and usually a distinct extension from the lateral exciple, frequently pigmented or even carbonized like the lateral exciple.
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