When two unrelated organisms living in a particular geographic area may show similar strategy, the phenomenon is called convergent evolution. Example: A desert has several types of drought resistant perennial plants called succulents. Example: Orchids, Euphorbia, Agaves, Aloes, Bryophyllum. All of them store mucilage and water. In some cases, succulents appear in stems . In some succulence appears in leaves. Succulence is required in desert plants to prevent drying up and retention of water.