Xerophytes
Xerophytes are sometimes loosely defineri as 'plants of dry habitats'. But others have defined xerophytes as 'plants which grow on the substratum that usually becomes depleted of water to a depth of at least 2 decimetres during a normal season'. Thus, in arid zones, all plants not confined to the margins of streams or lakes have been considered as xerophytes. In heavy rainfall regions shallow-rooted plants of sandy soils, plants of dry ridgepots, and algae, mosses and lichens which grow on tree bark, rock or similar surfaces. On the basis of their morphology, physiology and pattern of life cycle xerophytes are classified into drought evaders or drought escapers. They complete their life cycle within a short period when moisnue conditions are favourable but remain in form of seeds during dry unfavourable periods (e.g. Argemone mexicana. Solanum xanthocarpum) succulents (e.g. Opuntia sp., Euphorbia splendens) and non-succulents perennials (e.g. Calotropis procera, Acacia nelotica).