Peltate trichomes on biogenic silvery leaves of Elaeagnus umbellata.

Abstract

External and internal features of Elaeagnus umbellata leaves were investigated by optical and electron microscopy. The adaxial (upper) and abaxial (lower) leaf surfaces appeared green and silver in color, respectively. There were peltate trichomes on both the adaxial and abaxial leaf surfaces. The peltate trichomes were 200-300 μm in diameter and shield or umbrella-shaped. They had a central dome and 20-30 radiating rays that were fused to form a circular cap in the center and tapered at the end. The density of peltate trichomes was apparently higher on the abaxial leaf surface than on the adaxial leaf surface. At least two layers of peltate trichomes were commonly observed on the abaxial leaf surface. The epidermal cells on the abaxial leaf surface had convex lens-like shape in cross sections. No distinct chloroplasts were found in the cytoplasm of peltate trichomes. These results suggest that the silver coloration on the abaxial leaf surface is mostly due to structural coloration associated with the profuse overlapping peltate trichomes having a circular cap of radially fused rays. The shrub did not show any pigmentary cellular features associated with the silver coloration. With the silvery leaves as a reflective surface for shaded leaves in canopy, E. umbellata is likely to adapt to the harsh non-native light-demanding environments.