Notes: Symptoms that match those associated with Blastacervulus metrosideri are very common on Metrosideros excelsa wherever it grows in New Zealand. The literature cited in the Introduction shows that Eucalyptus has several superficially similar leaf-spotting fungi, and more intensive study of the M. excelsa associated fungi may reveal a greater diversity of species than currently recognised. For example, Teratosphaeria spp. were commonly detected from environmental DNA sequences from M. excelsa leaves (unpubl. data), and the symptoms caused by Teratosphaeria australiensis are similar to those associated with B. metrosideri (Sutton 1974, as Leptomelanconium australiense; Taylor et al. 2012). Commonly, the blastacervulus-like spots seen in the field are sterile, making a definitive identification based on morphology impossible.

The single, small specimen on Metrosideros umbellata (NZFS 5422) has markedly paler spots than those on M. excelsa and its acercvuli are smaller. Microscopically, this specimen appears to match those from M. excelsa. Additional specimens are needed to determine whether the macroscopic differences are consistent, and DNA sequences from a specimen on M. umbellata would confirm whether M. metrosideri occurs on more than one species of Metrosideros.

The holotype specimen was selected because a culture and DNA sequences were derived from it, but this specimen is not large. To examine the morphology, particularly nice specimens include PDD 30158 and PDD 116628.