The genus Acer, commonly known as maples, contains hundreds of species and cultivars. While most maples display reds and purples only in the fall, a select group of cultivated varieties maintain deep purple, maroon, or reddish-crimson leaves consistently throughout the growing season. This stable pigmentation offers a strong color contrast that lasts from spring until the leaves drop in late autumn. These trees are specifically bred to incorporate this rich, non-green hue as a permanent feature of their summer appearance.
Primary Maple Varieties with Purple Foliage
The most prominent purple-leaved maple is the ‘Crimson King’ Norway Maple (Acer platanoides ‘Crimson King’). This large, robust shade tree is known for its rich purplish-crimson leaves that hold their color consistently all summer, providing a striking contrast to green landscapes. The ‘Crimson King’ reaches heights of 30 to 40 feet with a similar spread. It is suitable for larger spaces and urban environments due to its tolerance for various soil conditions and city pollutants. Other similar Norway Maple cultivars offering all-season dark foliage include ‘Royal Red’ and ‘Goldsworth Purple’.
For gardeners seeking a smaller specimen, various cultivars of the Japanese Maple (Acer palmatum) are celebrated for their dark purple leaves. The ‘Bloodgood’ Japanese Maple is a popular choice, displaying deep reddish-purple foliage that deepens to a crimson red in the fall. Another notable variety is the ‘Purple Ghost’, which exhibits a deep lavender-purple leaf with distinct, dark veining, known as reticulation. The ‘Red Dragon’ cultivar features finely dissected, lace-like reddish-purple leaves on a weeping, mounding form. These Japanese Maple varieties are smaller, often maturing to heights between 8 and 20 feet, making them ideal for courtyards and container gardening.
How Maple Leaves Achieve Their Purple Hue
The purple pigmentation in these maple varieties is due to the constant presence of anthocyanins, which are water-soluble flavonoid pigments. Unlike carotenoids (yellow and orange pigments) that are present but masked by chlorophyll, anthocyanins are actively produced in the leaves. In most maples, anthocyanin production is only triggered in the autumn as the green chlorophyll breaks down.
In cultivars like ‘Crimson King’ and purple Japanese maples, a genetic mutation causes the tree to continuously produce and store high concentrations of these pigments within the cell vacuoles. This accumulation of anthocyanins overlays and effectively masks the green chlorophyll, resulting in the characteristic dark, year-round coloration. The precise shade of purple or red can also be affected by the pH of the cell sap; a higher pH often results in a more purple hue.
Environmental Factors Affecting Leaf Color Intensity
While the purple color is genetically determined, its intensity is significantly influenced by environmental conditions, particularly sunlight exposure. Full sun is required to maximize the production of anthocyanins, which the plant uses as a photoprotectant to shield the photosynthetic machinery from excess light. Maple leaves grown in full sunlight will exhibit the deepest, most vibrant purple color.
Conversely, leaves that are heavily shaded often appear greener or a duller bronze. This happens because the plant reduces the protective anthocyanin layer when light intensity is lower, allowing more underlying green chlorophyll to show through. For some Japanese Maple cultivars, a location receiving full morning sun but protected from intense afternoon heat may be necessary to prevent leaf scorch. Adequate moisture and a healthy root system are also important, as stress or nutrient deficiencies can alter pigment expression.