Seasonal dimorphism of foliage in Californian coastal sage scrub.

A pattern of seasonal variation in leaf size and position relative to the stem is reported for twelve mesophyllous shrubs in the coastal sage scrub of Mediterranean-climate areas of southern California. Leaves of reduced size, produced on axillary short shoots late in the growing season, persist through the dry season while many of the larger leaves on main stems are abscissed. The short-shoot leaves of Salivia mellifera have the same density thickness as those of the main stem, leaving open the question of whether the smaller summer leaves have physiological mechanisms for drought tolerance beyond a reduction in total transpiring surface. In Californian coastal shrublands seasonal dimorphism of leaves appears limited to mesophyllous shrubs. It is also found in analogues in comparable climatic regions of the Mediterranean, Chile and South Africa.