Colony characters can be distinctive and characteristic of a species. However,
colony appearance is difficult to describe with sufficient precision for it to be
very useful for identification. Growth rates in culture can be useful to distinguish
otherwise similar species. The production of conidia from effused conidiophores,
or from conidiophores aggregated into fascicles or pustules is usually characterisitic
of a species. Diffusable pigments can also be characteristic, although the colour of such pigments does not vary a great deal in Trichoderma. Strains referable to
section Longibrachiatum typically have conspicuous bright greenish-yellow pigments,
at least when first isolated. Dull yellowish pigments are common in many species,
but are not very distinctive. Some species are best characterized by a complete
lack of pigment in reverse, whereas reddish pigments occur in reverse in a few
isolates. Characteristic crystals produced in the media have been reported only for
Trichoderma aureoviride. Indistinct mouldy or musty odours are commonly produced
by different strains of Trichoderma. Characteristic aromatic odours resembling
coconut are produced commonly by strains of Trichoderma viride, and sometimes
also by Trichoderma atroviride.