P&PDL Picture of the Week for
May 3, 2010

Leaf characteristics of drought tolerant plants

Michael V. Mickelbart, Department of Horticulture & Landscape Architecture, Purdue University

There are certain characteristics that suggest the water stress tolerance of plants. Small leaves, leaf waxes, and minimal leaf area all lead to reduced water loss, and therefore, drought tolerance. However, it is always best to refer to reliable sources for lists of drought tolerant plants, such as the one created for this article.

Large leaf areas can be detrimental to growth and survival under conditions of water stress because there is more surface area from which water can be lost. Therefore, drought-tolerant plants will often have small leaves or, in the case of conifers, needles that have low surface area. While this is generally true, there are many plants with large leaf areas that are drought-tolerant, such as southern magnolia (Magnolia grandiflora), and sycamore (Platanus sp.).

Another way trees reduce leaf area is by having deeper sinuses. Sinuses are the indentations between lobes on a leaf. Trees that are more tolerant of dry conditions often have deep sinuses, which decrease their total leaf area.
Drought-tolerant plants often accumulate waxes on their leaves or needles. Waxes are thought to prevent water loss and reflect light, which keeps leaf temperature from becoming too high.

Leaf hairs (called trichomes) appear as grey or white pubescence and reflect light and reduce water loss. While we still don’t fully understand how trichomes affect plant water loss, leaves that are covered with these small hairs typically lose less water than those that do not.

Click image to enlarge

Spruce needles

Spruce needles

Maple sinuses

Maple sinuses

Holly waxy leaves

Holly waxy leaves

Trichomes on hydrangea

Hydrangea trichomes

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service