The influence of the material texture (substructure) on the force driving the crack tip in complex materials is analysed in a three–dimensional continuum setting. The theory proposed accounts for finite deformations and general coarse–grained morphological descriptors of the substructure. A modified expression of the J integral is obtained together with other path integrals which are necessary to treat cases in which the process zone around the tip has finite size. They allow also us to consider the influence of the presence of diffused interfaces in multiphase solids on crack propagation. The results can be applied to a very wide class of material substructures occurring in condensed matter. To indicate possible applications, the behaviour of cracks in ferroelectrics and in materials with strain–gradient effects is discussed: the specializations of the general results reduce to expressions that fit reasonably experimental data.