Seifert (1985) synonymised N. polythalama under the older epithet of N. pseudotrichia. Although somewhat similar especially in having muriform ascospores, N. polythalama is distinct from N. pseudotrichia. The lectotype specimen of N. polythalma has smooth ascospores unlike the spinulose ascospores of N. pseudotrichia (Fig. 59A–R, Fig. 60A–F). Characteristics of the asexual state are also useful in distinguishing these species. In the natural environment, the anamorph of N. polythalama produces dark purple conidial masses at the synnematal apex and the conidia of N. polythalama are larger than those of N. pseudotrichia (Fig. 59A–R, Fig. 60A–F). In culture, conidia of N. polythalama are swollen at both ends unlike those of N. pseudotrhicia. The optimum temperate for growth of N. polythalama on PDA is 25 °C while that for N. pseudotrichia is between 25 to 30 °C or 30 °C. Based on our phylogenetic analysis N. polythalama is clearly distinct from N. pseudotrichia with each species forming highly supported branches (Hirooka et al. 2010) (Fig. 1, Fig. 3).

Our phylogenetic results based on a multiple-locus analysis of 65 isolates from throughout the world support the monophyly of N. pseudotrichia with a second distinct clade from New Zealand. The New Zealand strains are herein recognised as Nectria polythalama, a name previously considered a synonym of N. pseudotrichia. Within Nectria pseudotrichia, six subclades exist that are strongly correlated with geography but these cannot be distinguished morphologically (Hirooka et al. 2010).