Citation: Pem D et al. (2019) Mycosphere Notes 275-324: A morphotaxonomic revision and typification of obscure Dothideomycetes genera (incertae sedis). Mycosphere 10(1), 1115–1246
Byssothecium Fuckel, Bot. Ztg. 19(no. 35): 251 (1861)
Saprobic or parasitic on Medicaginis sativae. Sexual morph: Ascomata pseudothecioid solitary, scattered, or in groups, immersed, semi-immersed to erumpent, globose to subglobose, black, apex with a short papilla. Peridium coriaceous, consisting of thick-walled, brown cells of textura angularis. Hamathecium composed of pseudoparaphyses, embedded in mucilage, branching, septate and anastomosing between and above the asci. Asci 8-spored, bitunicate, fissitunicate, cylindro-clavate, slightly curved when immature, pedicellate. Ascospores biseriate to uniseriate, fusiform, hyaline when immature, dark brown at maturity, 3- trans-septate, and variously ornamented. Asexual morph: Undetermined.
Type species – Byssothecium circinans Fuckel
Notes – The genus Byssothecium was introduced by Fuckel (1861) with the type species B. circinans. The latter was described as a saprobe or parasite of Medicago sativa (Semeniuk 1983) and a Pleospora-type centrum was observed (Boise 1983). A chaetophoma-like anamorph is reported in culture, however, no culture or herbarium specimen is listed (Boise 1983). Byssothecium was considered as closely related to Teichospora (Boise 1983). Later, it was accepted as a genus in Massarinaceae by Zhang et al. (2009). Some studies showed that Byssothecium was distinct from Massarinaceae and was placed in Dothideomycetes genera incertae sedis (Lumbsch & Huhndorf 2010, Wijayawardene et al. 2014). However, in the phylogenetic analysis done by Chethana et al. (2015) and Thambugala et al. (2015), Byssothecium clustered in Massarinaceae. Currently, the genus consists of eight species (Index fungorum 2019). The asexual morph is coelomycetous (Wijayawardene et al. 2017). Cultures and sequences are available for B. circinans however, it could not be accommodated in any family so far (Wijayawardene et al. 2018). We examined the isotype specimen of B. circinans and according to morphological characters, B. circinans share morphological similarities to species in Trematosphaeriaceae such as subglobose, black, coriaceous ascomata, thick-walled cells of textura angularis, septate, cellular pseudoparaphyses, embedded in mucilage, branching and anastomosing between and above the asci, cylindric-clavate bitunicate asci and brown fusiform ascospores. But, based on a megablast search using the LSU sequence of Byssothecium circinans, the closest matches in NCBI’s GenBank nucleotide database were Helminthosporium juglandinum (L97), Helminthosporium juglandinum (L118), Helminthosporium juglandinum (L101) with 100%, 99%, 99% similarities respectively with 0% gaps. Phylogenetic analyses of the putative strain of Byssothecium circinans (CBS 675.92) available in GenBank shows that Byssothecium forms a lineage basal to Pseudodidymosphaeria spartii (CBS 183.58) (Fig. 8). Byssothecium resembles Pseudodidymosphaeria in having semi-immersed ascomata, however, it differs from other morphological characters. The genus Byssothecium rather resembles species of Pseudosplanchonema in having pseudothecioid ascomata and cylindro-clavate asci but differs in ascospores characters (3- trans-septate vs 1-sub-median septate, pseudosepta between the guttules). We therefore, place Byssothecium in Massarinaceae.