Mediterranean climate areas such as Southern California cover less than 2% of the earth’s surface, yet contain nearly 20% of the known plant species in the world. These ecosystems are a worldwide conservation priority, and their ability to go dormant – in some cases, “brown” – over the summer is critical to their survival through the dry season. The dormant state of many perennial plants is an excellent survival adaptation that allows them to conserve energy and water.
The unique leaf shape of each plant also contributes to its response to changing temperatures. The laurel sumac has large, folded leaves that are often described as “taco-shaped.” The folded shape of this leaf helps reduce the amount of surface area exposed to sunlight and therefore limits moisture evaporation, helping the plant conserve water over the dry summer. The coast live oak tree has several pointy edges around its holly-shaped leaves, which gather up dew from the misty marine layer of “June Gloom.” As the water condenses, it rolls along the surface of the leaf, beading up and falling like rain to the roots below. Even the tiny feather-like leaves of the California sagebrush require very little water, and can become “drought deciduous,” with the normally evergreen plant dropping its tiny leaves to survive a hot summer.
One plant that changes dramatically through the seasons is poison oak – one you will definitely want to learn to identify. Poison oak is typically found in shaded areas or along streams, and is plentiful along the trails in the Buck Gully Preserve in Newport Beach. Poison oak has adapted to grow just about anywhere, so it is useful to not only know where it grows, but what it looks like.
True to its scientific name, Toxicodendron diversilobum, poison oak can be found in a variety of forms, from groundcover vines to large shrubs. And if you’ve heard the old adage: “Leaves of three; let it be,” you know that this highly toxic plant’s lobed leaves grow in groups of three along the stem. In early summer, the leaves are bright green, with some changing to a greenish-yellow or reddish color as the season ends. By fall, the leaves are brick red, and after the plant drops its leaves, only a mass of bare vines or stems is left in the winter. Identifying where poison oak lives in the summer will help you avoid it near trails all year round.
Who says we don’t have seasons in Southern California? As you enjoy late-blooming wildflowers such as lupine and deerweed, take note of how other native plants prepare for the hot months ahead. Learning how each little leaf adapts to changes in the weather can help you appreciate the Mediterranean climate of our local ecosystem.