Argillaceous rock is a type of sedimentary rock that contains clay components. It is often used in bonsai to create dramatic landscapes, such as cliffs or mountains, where the trees grow on or in the rocks. There are two main styles of rock bonsai: Seki-joju, where the roots of the tree wrap around the rock and reach the soil below, and Ishisuki, where the roots are confined within the rock or a container. Argillaceous rock is suitable for bonsai because it breaks down easily when untreated, allowing the roots to penetrate and absorb water and nutrients. However, it also requires careful watering and fertilizing to prevent root rot or nutrient deficiency. Some examples of trees that can grow on argillaceous rock are pines, junipers, maples and azaleas.