A high-resolution SEM examination of the warty layer in tracheids of the Australasian softwood genus Callitris Vent. has revea1ed that warts in 12 of the 16 species have variable, complex morphology and nodule-like projections, giving them a 'nodulated' or 'branched' appearance similar to those described for certain hardwoods. Pairs of warts were occasionally anastomosed. Warts could be categorised into two types; large and no dulated, or small and hemispherical. In the four Callitris species native to high rainfall environments, warts were invariably of the latter type and were morphologically distinct from the mixed populations of small hemispherical and large nodulated warts found in species from dry habitats. This suggests that large nodulated warts are of adaptive value in waterstress conditions. Wart morphology was useful as an indicator of Callitris species although intra-specific variation limited the accuracy of diagnosis.