What exactly is Trichoderma harzianum?

Trichoderma harzianum is neotypified by an isolate from the type locality, and this neotype is fully described. It is compared with original herbarium specimens and recent isolates of T. atroviride P. Karsten, one of which is designated as epitype. RFLP analyses of the internal transcribed spacer (ITS) region of the rDNA gene cluster, and sequence analysis of the ITS1 region were used to group these and other isolates received as T. harzianum. Two major groups were found. The first group, the T. harzianum complex, comprises the neotype and other isolates from the type locality, Okuda group 2 isolates, Muthumeenakshi group Th1 mushroom isolates, some isolates used in biological control, the ex-type culture of T. inhamatum, and the aggressive mushroom competitor the Muthumeenakshi group Th2. The latter forms a distinct subgroup of group 1 on the basis of unique RFLP and ITS1 sequence types (six base pairs different); it will be taxonomically distinguished from ?: harzianum in a forthcoming paper. The name T. harzianum requires conservation because of the existence of two obscure older names for the same taxon, the ex-type cultures of which fall also in the first group. The second group, the T. viride-T. atroviride complex, comprises Okuda group 1 and Muthumeenakshi group Th3 isolates.