The Syringa genus, commonly known as lilac, is a popular ornamental shrub prized for its dense clusters of highly fragrant flowers that appear in spring. While the name suggests a single, pale purple shade, lilacs display a remarkably broad spectrum of hues. These colors range from the familiar purple to pure white, and extend into shades of pink, magenta, and yellow. This diversity in coloration is a result of centuries of cultivation and hybridization.
The Core Color Spectrum
The most recognizable coloration is the namesake lilac, which falls under the broader category of purple and violet shades. This spectrum includes pale, silvery-lavender blooms, extending to much deeper tones like violet and amethyst. Cultivars like ‘President Lincoln’ are often cited as producing flowers closest to a true, saturated purple.
Another dominant color group is white, which is visually striking against the shrub’s dark green foliage. White lilacs, such as Syringa vulgaris ‘Vestale’, result from a complete lack of pigment production in the flower petals. This absence of color provides a clean, bright contrast to pigmented varieties in a garden setting.
The third primary color is pink, spanning from very pale blush tones to more intense rose-pink shades. The cultivar ‘Katherine Havemeyer’, a classic French Hybrid, is known for its large, double flowers in a distinctive pink-lavender combination. These three core colors—purple, white, and pink—form the foundation of the species’ color identity.
Nuances in Lilac Hues
Beyond the most common colors, lilac breeders have developed many cultivars exhibiting subtle shades that challenge traditional classification. The “blue” lilac category rarely features a true sky-blue; instead, these flowers are typically a lavender-blue or purplish-blue. The cultivar ‘Nadezhda’ is an example of a double-flowered form where the purple buds open to reveal distinct bluish florets.
Deep reddish and magenta hues represent the most saturated end of the color spectrum and are often grouped separately from the lighter purples and pinks. Cultivars like ‘Andenken an Ludwig Späth’ display a rich, deep reddish-purple, while ‘Charles Joly’ is known for its vibrant, dark magenta blossoms. These intense colors are valued for the visual impact they make in the landscape.
The Royal Horticultural Society (RHS) and specialized lilac registries employ a detailed classification system to categorize these subtle differences. This system acknowledges seven distinct color groups:
- White
- Violet
- Blue
- Lilac
- Pink
- Magenta
- Purple
One of the rarest colorations is the yellow or cream variety, such as Syringa vulgaris ‘Primrose’. These flowers shift from a buttery yellow in bud to a paler cream as they fully open.
The Science Behind Lilac Pigmentation
The wide array of colors in lilac flowers is primarily controlled by a class of water-soluble pigments called anthocyanins. These flavonoids reside within the plant’s cell vacuoles and are responsible for nearly all red, purple, and blue coloration. The specific hue expressed is determined by the molecular structure of the anthocyanin compounds present.
Flowers expressing purple and blue tones contain derivatives of delphinidin, while the redder and pinker shades are often linked to cyanidin derivatives. The precise combination and concentration of these two main types of pigments create the entire gradient from magenta through lilac to violet. For instance, the deep magenta cultivars have a higher concentration of the red-leaning anthocyanins.
The color expression is also influenced by the acidity or alkalinity (pH) of the cell sap inside the flower petals. Anthocyanins are naturally pH-sensitive, shifting towards red in acidic environments and towards blue in alkaline environments. The slightly alkaline soil conditions preferred by Syringa species can favor the expression of bluer tones within the purple-to-blue range.