Plant Coloration

Submitted by: Mike Kay,
Maryland Forest Service
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Have you ever wondered why plants are the color that they are?  As we know, most plants leaves are green in coloration; however, some varieties can be yellow, red, blue, and even purple.  The reason for these various colorations depends on the three major chemicals found in leaves,  chlorophyll – green, anthocyanins - red, blue, purple and carotenoid  pigments yellow, orange, red.  Most leaves have all of these pigments but in different concentrations so that the color of the leaf is dependent on the relative concentrations of these pigments.  Over the years Horticulturists have cultured plants to produce various foliage colors by selective breeding and now you have a multitude of colors like purple leaf plum, variegated holly, blue atlas cedar, and Japanese maple to name a few.  In most cases the secondary color becomes more distinct when the plant is in full sunlight so if you want your Crimson King Maple to look crimson it should be placed out in the open.

The purple color of this purple leaf plum is due to an abundance of anthocyanins in the foliage.

Many new leaves that are unfurling have a reddish color and eventually turn to green once they enlarge.  In this instance the leaf has more anthocyan pigments to start with then chlorophyll develops.  A possible adaptive reason for this according to scientists is that many insects and plant eating animals do not see in the red and purple spectrum very well so the new leaves are camouflaged or they look gray an unappealing to animals that would  otherwise consume them.  Avoiding this damage will allow these leaves to expand and feed the plant.  Once the leaf has expanded its role is to trap sunlight and produce energy for the plant so that chlorophyll becomes dominant and the leaf turns green.  Also, when a plant is lacking nutrients that it needs to survive like iron and nitrogen it is in a weakened state and can not produce the chlorophyll that it needs so that other pigments like carotenoid become dominant and the leaf turns yellow or dull in appearance.  The changing color of autumn foliage is also due to the gradual separation of the leaf from the plant resulting in the loss of chlorophyll. Of all the colors in nature the color blue is the rarest and it is most prevalent in plants that inhabit arid conditions.  A reason for this bluish color is waxy chemicals and lipids that protect the plant from water loss called antidessicants that are found on the exterior of the leaf.  Thus the blue color results as an adaptive measure to help the plant retain moisture and survive in dry areas.

The blue color in this Atlas cedar is an adaptation for growing in dry conditions.