The interaction of plants with concrete structures in manners which can be problematic are both chemical and physical. However, most physical damage primarily derives from larger plants. For algae to be brought into contact with a concrete surface, there must be some movement of algae-bearing water past the surface. The rate of flow plays an important role in the rate at which algae become attached to this surface. Vascular plants have been proposed that higher plants may become established on concrete surfaces through two mechanisms. The first mechanism occurs on both horizontal and vertical surfaces and involves seeds of plants becoming lodged in cracks or holes in the surface. The second mechanism requires the establishment of moss on a horizontal concrete surface. Algae are generally sensitive to pH, with acidic and alkaline environments limiting growth. There have been a limited number of studies on the characterisation of bryophyte species growing on concrete surfaces.