Red chlorophyll is a rare red pigment found in a very small percentage of marine plants. Like green chlorophyll, it allows the plants to absorb light to begin photosynthesis, the process by which plants convert energy into food. Plants containing red chlorophyll typically fall into the category of cyanobacteria, or microscopic plants that grow in small colonies on coral reefs and stationary marine animals, like sea squirts.
One particular species of cyanobacterium contains red chlorophyll, also classified as chlorophyll d or chlorophyll f. Called Acaryochloris marina, these cyanobacteria appear red in color, making them unlike the rest of their species. The ancient Greeks gave cyanobacteria their name because cyano means ‘blue-green.’ Acaryochloris marina does not share this color trait, but shares the same cellular structure, growth patterns, and environmental needs as the rest of its species. Cyanobacteria filled with this chlorophyll can also grow at lower depths than its blue-green cousins.
This variety of marine flora shows up red on the light spectrum because it absorbs infrared light on the extreme end of the light spectrum and reflects visible red light. Infrared light wavelengths are much longer than those in the visible spectrum, allowing them to penetrate deep into the ocean. Most other lights, especially the blues and purples on the short end of the spectrum, are filtered out of the light that travels into the water. If Acaryochloris marina could not absorb infrared light, it could not survive.
There are two kinds of red chlorophyll: chlorophyll d and chlorophyll f. The first kind absorbs infrared light just outside of the visible spectrum, generally measuring 700 wavelengths or more. The second variety absorbs infrared light in the 800 wavelength range and higher. Plants containing chlorophyll f can survive deeper in the ocean than those containing chlorophyll d, though both kinds of chlorophyll require sunlight.
Scientists interested in genetically engineering plants are trying to find a way to make ordinary farmers’ crops produce red chlorophyll. Above the water, red chlorophyll would, theoretically, absorb much more sunlight than green chlorophyll. Green chlorophyll absorbs blue and purple rays of light on the short side of the visible light spectrum, meaning that the rays it absorbs aren’t as strong as red and infrared light. Terrestrial plants able to absorb long, strong infrared rays of light might be able to photosynthesize at a very high rate, meaning they would mature and produce crops very quickly.