Past controversy about relationships of Metacapnodiaceae was partially resolved by increasingly sophisticated observations on the development of the ascomata, and reinforced more recently by molecular systematics. Hughes (1972) first erected Metacapnodiaceae S. Hughes & Corlett in order Pleosporales on the basis of what Corlett (1970) interpreted as a Pleospora-type centrum, characterized by pseudoparaphyses that grew from the ceiling of the reproductive cavity downward among the asci. This character, together with tapering hyphal tips and superficial conidiogenous cells separated Metacapnodiaceae from other sooty molds in other families, notably Capnodiaceae, which have a Dothidea-type centrum, cylindrical hyphae, and pycnidial asexual forms (Corlett et al. 1973). However, Corlett (1970) noted that the pseudoparaphyses of the Metacapnodium juniperi centrum were slightly atypical for Pleosporales because they did not reach the bottom of the cavity and instead persisted only at the top of the locule. Barr (1979) considered that these short pseudoparaphyes, or paraphysoids indicated deep phylogenetic separation from Pleosporales, and erected Chaetothyriales, a new order, for the perithecioid fungi that have them. Winka et al. (1998) used ribosomal DNA evidence to show that members of the Chaetothyriales were indeed distantly related to Pleosporales. Hawksworth and Boluda (2020) determined the first ITS sequences for Metacapnodium ericophilum, and their analysis placed Metacapnodium in Eurotiomycetes, somewhere near Phaeomoniellales and Chaetothyriales. Based on nrSSU phylogenetic analysis, Sugiyama et al. (2020) inferred that Metacapnodium neesii was the sister to all of their examined taxa in Chaetothyriales, with high bootstrap support. Having established M. neesii in pure culture facilitated sequencing not only of its 479 bp ITS region but also of 900 bp from the 5’ end of the ribosomal large subunit gene (nuLSU), 1074 bp of the 5’ end of the ribosomal small subunit gene (nuSSU), 777 bp of the gene encoding the polymerase II second largest subunit (rpb2), and 892 bp of the gene encoding the elongation factor 1–alpha (ef1-α) (Sugiyama et al. 2020). These Sugiyama et al. (2020) sequences contributed to our ability to select or design Metacapnodium specific primers in this study.
After decades of confusion, integration of names of sexual and asexual forms of Metacapnodium has largely been resolved. Rossman et al. (2016) recommended conserving Metacapnodium Speg. 1918 against Antennularia Rchb. 1828. Following this recommendation, Metacapnodium has been approved for protected status under Article F.2.1 of the International Commission on the Taxonomy of Fungi and the Nomenclature Committee for Fungi against Antennularia, and against other names for the sexual or asexual forms that were not formally considered (May 2024). This leaves open a biological question of whether all species once classified only as asexual forms including Capnobotrys, Capnocybe, Capnophialophora, and Capnosporium should be transferred to Metacapnodium.
Investigating systematics of Metacapnodiaceae still poses significant challenges. Firstly, multiple species of sooty molds can inhabit the same subiculum (Hughes 1972; Hughes and Seifert 2012). Isolating sooty molds in Metacapnodiaceae into pure culture has been challenging. The lack of living cultures has made the resolution of phylogenetic relationships in Capnodiales and Metacapnodiaceae difficult (Crous et al. 2009). Because of these challenges, much of the richness in diversity of Metacapnodiaceae has yet to be discovered and the phylogenetic positions of the family and its species remain only partially resolved.