Encelia farinosa

 Encelia farinosa (brittlebush) (incienso)

Asteraceae

• One way in which the leaves of desert plants reduce the amount of solar radiation they receive is through leaf surface hairs, scales, or waxes that increase the reflectance of solar radiation. Pronounce grey or white leaves reflect more light than green or greenish leaves and thus have reduced levels of light energy reaching the leaf structures. One of the best regional examples is seen with brittlebush. In the spring, when soil water is available, brittlebush produces relative broad and thin leaves with a modest coverage of hairs (pubescence) on their surface. As drought stress gradually increases, brittlebush forms smaller and thicker leaves with a dense covering of silver hairs. Looking in cross-section the mass of hair on both the upper and lower leaf surfaces may be greater than the thickness of the leaf itself. These reflective hairs cut up to half of the solar radiation that would otherwise be absorbed by the leaf surface. The result is a cooler leaf with a reduced loss of water through transpiration, but at a cost of reduced rates of photosynthesis.
• Third in importance is brittlebush. It is a familiar and conspicuous shrub that colors broad areas of the desert plains in the spring with its large, radiate yellow flowers. It is easily recognized as a tall shrub up to 5 feet in height, often with multiple main stems, displaying large lemon-yellow sunflowers. Brittlebush is a classic species for describing seasonal leaf dimorphism. The early spring leaves of brittlebush are broad and thin with a light white pubescence. As the season progresses and water stress increases, the newly produced leaves become smaller, thicker, and have and increased density of hairs on their surface. Leaves are ultimately shed under conditions of summer drought stress. A unique character of brittlebush, in comparison to its related species, is that several flower heads are born on each stem, Other Encelia species have just a single flower head per stem. 
• Brittlebush frequently forms hybrids with button encelia (Encelia frutescens), as well as with California encelia (Encelia californica).
• Although it avoids higher higher elevations above 3, 000 feet, the range of brittlebush extends from creosote bush scrub in Death Valley across the Mojave Desert and all through the Sonoran Desert into Mexico. Over this range it shows preference for rocky well-drained soils on south-facing slopes. "California Desert Plants, Philp W. Rundel, Robert J. Gustafson, Michael E. Kauffmann."