Plant coloration

Have you ever wondered why plants are the color that they are? While most leaves are green, some varieties can be yellow, red, blue, and even purple.

The color is determined by three major chemicals: chlorophyll – green; anthocyanin — red, blue, and purple; and carotenoid pigments — yellow, orange, and red. Most leaves have all of these, but in varying amounts so that the color of the leaf is dependent on the relative concentration of these pigments.

Over the years, horticulturists have developed plants to produce various foliage colors by selective breeding, and there are 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.

Many new leaves that are unfurling have a reddish color and eventually turn to green once they are fully open. In this instance, the leaf’s anthocyanin pigments are predominant before 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 either not discernible or they look gray and 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 cannot 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, blue is the rarest and it is most prevalent in plants that inhabit arid conditions. Blue is often the result of waxy chemicals and lipids, antidessicants, that protect the plant from water loss on the exterior of the leaf. This blue is the result of 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. Photo was taken in the Myersville area.

Nature Note for 10/30/2016

Article and photo by Mike Kay, Forester for Frederick County