The characteristic features of formation of mixed crystals in solutions and the basic concept underlying these processes were established in [J. Crystal Growth. 255 (2003) 150; J. Crystal Growth. 172 (1996) 226; Zap. Vses. Mineral. O. (1983) 742; Zap. Vseross. Mineral. O. (1991) 3; Zh. Struct. Khim. (1994) 79]. The present study is a continuation of the complex research of morphology and defects of potassium acid phthalate-rubidium acid phthalate (KAP-RbAP) mixed crystals that are formed in aqueous solutions. The most important characteristic of this series is the formation of heteroepitaxial porous and continuous textures as a result of the exchange reaction between the crystal and the "foreign" solution. The interaction of KAP and RbAP crystals with aqueous solutions saturated with RbAP and KAP, respectively, is studied. The corresponding processes were observed both in situ and ex situ with optical and atomic force microscopes. The results obtained were used to develop the theoretical model of formation of specific morphological textures in liquid-phase heteroepitaxy, including the textures formed in aqueous solutions of various salts. (C) 2003 Elsevier B.V. All rights reserved.