ABSTRACTNeurospora intermediais found on burned substrates in all tropical and subtropical areas that have been sampled in both Eastern and Western Hemispheres. Cultures from burned substrates are salmon orange and are virtually indistinguishable in appearance from typical strains ofN. crassaandN. sitophila.A second, distinctN. intermediaecotype is found almost exclusively on nonburned substrates and only in the Eastern Hemisphere. This type is saffron yellow rather than salmon orange, with conidia that are significantly larger than those of the other type. The two ecotypes are conspecific on the basis of intercross fertility, although strains of the yellow type show reduced fertility both among themselves and in crosses with orange strains. The visible differences between the types are due to multiple genes which are not tightly linked.