The presence of both purple and green coloration on a single plant’s leaves is a striking visual feature. This bicolored effect results from the simultaneous presence of two distinct classes of pigments in the foliage. This dual pigmentation is either a genetic variation or a natural adaptation.
The Chemistry Behind Purple and Green Leaves
The green color is derived from chlorophyll, the pigment responsible for capturing light energy necessary for photosynthesis. Chlorophyll absorbs red and blue light wavelengths while reflecting green light, which the human eye perceives. This pigment is typically dominant and located within the chloroplasts inside the plant’s cells.
The purple, red, or blue hues, however, come from a different group of water-soluble pigments known as anthocyanins. These pigments are typically stored in the cell’s central vacuole, separate from the chlorophyll. When anthocyanins are present in high concentrations, they can mask the green color of the underlying chlorophyll, resulting in a distinctly purple appearance. Anthocyanins absorb light in the green and yellow wavebands, which helps filter out excess light that could potentially damage the photosynthetic apparatus, effectively acting as an internal sunscreen.
Common Indoor and Garden Varieties
Many species popular in indoor and outdoor settings display these dual colors. A widely known indoor example is the Wandering Jew (Tradescantia zebrina), which features lance-shaped leaves with prominent stripes of silver-green and deep purple. Certain Calathea varieties, like the Rose-Painted Calathea (Calathea roseopicta), show green and white markings on top, while the entire underside is a rich magenta or purple. This purple underside is believed to help the plant capture scattered light in its shaded, native habitat.
The Purple Shamrock (Oxalis triangularis) also presents a striking purple and green combination, featuring deep violet, clover-like leaves that fold up at night. The green is often only visible as a subtle highlight or thin margin. For garden settings, the Persian Shield (Strobilanthes dyerianus) is favored for its iridescent, metallic purple leaves with contrasting dark green veins and margins.
The popular bedding plant, Coleus (Coleus scutellarioides), offers many cultivars featuring complex patterns of purple, lime green, and dark green variegation. The Rex Begonia is also prized for foliage that frequently displays swirling bands, spots, and zones of silver, emerald green, and deep burgundy-purple. These examples show that the purple and green combination can appear as stripes, variegation, or as a color contrast between the top and bottom surfaces of the leaf.
Environmental Triggers for Color Intensity
The intensity of the purple hue is often influenced by specific environmental conditions. Light exposure is a primary trigger, as high light levels stimulate the plant to produce more anthocyanin pigments. This increased pigmentation serves a photoprotective role, shielding the chlorophyll from damage caused by excessive visible and ultraviolet light. A plant grown in bright light usually exhibits a deeper, more vibrant purple color compared to one grown in low light.
Temperature is another factor, as cooler temperatures can also induce the accumulation of anthocyanins. This response is noticeable in many deciduous trees during autumn, but also applies to perennial and garden varieties. Low temperatures may cause a temporary increase in purple pigment to protect against cold stress. Other stressors, such as nutrient deficiencies, particularly phosphorus or nitrogen, can also lead to increased purple coloration as a physiological response.