C) Brittlebush
The brittlebush (Encelia farinosa) is a common desert native. It's whitish appearance is caused by a dense covering of soft hairs protecting a dark green leaf. This adaptation helps reflect sunlight--and therefore heat--off of the plant. The tiny hairs also help to insulate the plant from water loss. Brittlebush further reduces water loss by dropping its leaves at the first sign of water stress. As the leaves degrade into the soil, a chemical is released to prevent other plants from growing in close competition for the remaining water in the soil. It gets its name from this behavior, during its leafless dormancy, the plant becomes very brittle (but easily recovers after rain).
http://www.tarleton.edu/~range/Shrublands/Sonora%20Desert/sonorandesert.html