Drought-tolerance

Water, ninety percent or more of total plant weight, is essential for plant operations. Strong solar radiation with high light intensities results in increased evaporation from soil and transpiration from plants. While temperate climate plants need good supplies to cool surfaces, Mediterranean natives maintain their water balance through their own combinations of adaptive qualities. By reduced transpiration they can survive with little or no water other than rainfall, storing it too.

Evergreen leaves, often hard and spiny to touch, are characteristic to many Mediterranean plant families. They reduce water loss by a choice of adaptations. These include active ones, such as closing their leaf openings, as well as passive ones. A thick cuticle is often combined with light-reflecting waxy coating. Microscopic scales give plants a whitish or greyish tint, highly effective in reflecting light and heat.

Careful leaf-positioning, another feature, creates within the plant a favourable shade centre. It may also, in contrast, avoid leaf exposure to sun. Many legumes close up leaves during the day, others hold them vertically.

Leaf reduction is common, achieved by scales in all sizes and shapes, but also by narrow leaves. Often blade surface is limited to bits of tissue along needle-like leaves. Many species feature dissected leaves.

Leaf protection is achieved by adaptations which cool the surface. The secretion of a water-repellent, gaseous layer conserves water vapour pressure on leaf surfaces.

Many plants, including bulbs, have evolved life cycles that include summer deciduousness and dormancy. Others, in a summer-dormant, green yet leafless state, confine photosynthesis to stems. This is often combined with the conversion of the branch tips into protective spines.

Efficient water storage is widely used by succulents which store water in thickened stems, leaves or roots and harden the skin to seal it in.

Through one or more of these adaptations plants cope with dry summers. In the fight for survival every species chooses its tricks and weapons. But whatever method they use, the result is to retain precious water and survive.