Why are Some Leaves Not Green?

April 24, 2020


Menashe_Plactrantus mona (002)

Photographer: Menashe Davidson 
Summary Author: Menashe Davidson 

Plants are green because they contain the pigment chlorophyll. This pigment primarily absorbs light in the red part of the visible spectrum (long wavelengths), but light is also absorbed in the blue region (short wavelengths). Green light isn’t as readily absorbed, it’s mostly reflected, so the plant appears green.

The surface of the leaves on the upper row of the top photo looks greener than the leaves on the bottom row because they contain more chlorophyll – more sunlight is trapped by the upper surface than the bottom surface. Plants that have other colors contain pigments that trump the chlorophyll. In the case of the purple colors of the Plectranthus plant (bottom row of top photo, at far left, and also the second photo), the lower surface of its leaves contains a higher concentration of anthocyanin than chlorophyll, which is less adept at absorbing red light.

Photos of the leaves from the ornamental plants on the top photo were taken on May 2, 2019. The second photo of Plectranthus was taken on April 9, 2020. Both were snapped in my apartment garden in Rishon LeẔiyyon, Israel. Note that on the second photo, both the upper and lower sides of the same leaf (at right), and their different colors, can be seen.