Flowers produce a variety of biological pigments as sources of color. Carotenoids, such as beta-carotene and xanthophylls, are produced and stored in chromoplasts—the orange organelles seen inside these petal cells. The red, purple, and pink anthocyanins are produced by petal cells and stored in the vacuole, which takes up most of the cell's volume. Together, the orange chromoplasts and hot pink anthocyanins make this Calibrachoa flower, a relative of petunias, look red to us and to pollinating animals. The cone shaped cells of the epidermis at the top of the image are responsible for the velvety look of the petals and may provide additional visual and tactile signals to pollinators—like landing on a soft red carpet.
The epidermis of the red petal of a Calibrachoa flower was peeled from the flower, mounted in water on a glass slide, and viewed with a light microscope.
Stacey D. Smith PhD., Dept. Ecology and Evolutionary Biology, University of Colorado at Boulder.