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.

Specimen examined. New Zealand. South Island, Westland District, Granville Forest, Orwell Creek, on leaves of Nothofagus fusca, 2 Apr 1963, S.J. Hughes, from slides prepared by S.J. Hughes, from mixed collection, DAOM 106914 (Capnobotrys atro-olivaceus isotype).
Description. The dark brown to black, velutinous subiculum of this specimen included abundant Metacapnodium australis. However, the several permanent slides associated with the specimen did contain M. atro-olivaceus. Mycelium of moniliform hyphae, olive-brown and densely verrucose throughout, warts coarse, prominent, dark olive-brown. Hyphae straight to curved, anastomosing, with lateral branching, tapering toward the ends, cells globose, as long as or broader than wide, to 16 μm wide, narrowing to 3.5–5 μm at the hyphal tips.
Notes. Metacapnodium atro-olivaceus can be distinguished from other species with similar capnobotrys forms by its dark olive brown color, prominent, dark-colored verrucae, the subcylindrical rather than funnel-shaped collarettes on its phialides, and as exemplified by Fig. 5B, its mature hyphal cells are narrower than those of many other Metacapnodium species.

Specimen examined. New Zealand • South Island, Westland District, Granville Forest, Orwell Creek, on leaves of Nothofagus fusca., 2 Apr 1963, S.J. Hughes, from mixed collection, DAOM 106914 (C. atro-olivaceus isotype).
Notes. The mature hyphae of M. australis and Capnobotrys atro-olivaceus that are intermingled mycelia in the subiculum of DAOM 106914 differ in diameter and color. Hyphae of M. australis are up to 29 µm wide and are brown without olivaceous tints, while mature hyphae of C. atro-olivaceus are up to 16.2 µm wide and are “dull, dark olivaceous brown” (Hughes 1981).
In the ITS phylogeny, M. australis appears as sister to M. dingleyae (Fig. 2). Hughes (1981) distinguishes M. australis from three similar species: Capnobotrys laterivecta, C. paucisporus, and M. dingleyae that share a capnobotrys form and curved hyphae with upwardly curving or straight branches that arise at right angles, and more or less doliiform component cells. Most similar to M. australis is C. laterivecta, which can be distinguished from M. australis by its larger conidia and by the unusual attachment of its conidia by their long sides, just below their septa, to conidiogenous cells (Hughes 1981). Metacapnodium australis has smaller conidia and a larger number of conidiogenous cells at hyphal tips compared to C. paucisporus. Metacapnodium dingleyae can be easily distinguished by the presence of conidia with more than one septum (Hughes 1981). The prominent constrictions at the septa and coarse warts on capnobotrys conidia of M. australis help distinguish this species from others with capnobotrys forms, including M. moniliforme.

Here, with the goal of better characterizing species diversity, we determined complete or partial DNA sequence barcodes for ribosomal internal transcribed spacer (ITS) regions for 16 collections of Metacapnodium using a Metacapnodium-specific primer, followed by phylogenetic and morphological analyses. Tapering, moniliform hyphae, cells wider than long, and a distinctive phialidic asexual state were good predictors of membership in a well-supported Metacapnodium clade. Sequences from the 16 collections represent 9 named species of Metacapnodium.