In recent DNA-based cladograms of dicotyledons, Aextoxicaceae (one sp., Chile) and Berberidopsidaceae (three spp., Chile and Australia) form an isolated clade, Berberidopsidales, basal to rosids and asterids. Until recently, Aextoxicaceae had been placed in Euphorbiales, Berberidopsidaceae in Violales. Light microscopy and scanning electron microscopy (SEM) studies of wood of the two families show numerous shared primitive features: perforation plates with numerous bars and extensive pit-membrane remnants, lateral wall pitting of vessels scalariform to transitional, tracheids present; long vessel elements and tracheids, low F/V ratio; diffuse axial parenchyma; and Heterogeneous Type I rays. Features reported for the first time include crystals with various degrees of encapsulation in ray cells (Aextoxicon), pit membrane remnants in perforations (Berberidopsis, previously reported in Aextoxicon), and presence of narrow latewood vessels the perforation plates of which can bear pit membranes (Berberidopsis). Probable synapomorphies of the two families include marked difference between multiseriate parts (cells procumbent only) and uniseriate parts (cells square to upright), and presence of dark-staining deposits in axial parenchyma and rays. Cladistics does not use symplesiomorphies, which are numerous between the two families, to group closely-related families at clade tips. Ecological and habital adaptations of woods of the two families are briefly considered.