Plants harvest solar energy from sunlight and convert it to chemical energy (e.g. sugar) in a process called photosynthesis. This process occurs in the green parts of plants. Plants are green because they contain a green chemical pigment called chlorophyll, and it is found in microscopic structures called chloroplasts. Photosynthesis occurs in the chloroplasts. Sometimes leaves contain other pigments besides chlorophyll, and these may cause the leaves to be various shades of red, orange, yellow, or combinations of colors like we find in the leaves of crotons.
Most plants produce specialized photosynthetic organs, called leaves, which are usually flat and thin and are efficient at intercepting sunlight. Leaves are attached to plant stems. Leaves can be used to help us identify plants, because each kind of plant produces leaves characteristic of that particular plant. Some kinds of plants (e.g., most cacti and a number of euphorbias) don’t bear leaves on mature stems, but, instead, photosynthesize with their green stems. Figure 1 shows a shoot of a Euphorbia with a few very small leaves that fall off the shoot shortly after they form, leaving it leafless at maturity.
Figure 2 shows a stem pad of prickly pear cactus with a few yellowish small tubular leaves that fall off the stem shortly after they form, leaving it leafless at maturity.
Come to the World Botanical Gardens and see examples of all of these and more with one of our fun and exciting garden tours!
Dr. Lanny Neel, Garden Director Emeritus, World Botanical Gardens