The Dahlia variabilis is a highly cultivated flowering plant, celebrated for its astonishing range of colors and forms. Native to the high elevations of Mexico and Central America, this perennial species has been bred into over 20,000 different cultivars since its introduction to Europe in the late 18th century. The plant’s unusual genetics, which include an octoploid chromosomal structure, allow for a vast diversity that results in intensely saturated hues across almost the entire visible spectrum.
The Full Spectrum of Available Hues
Dahlias showcase a breadth of color that includes all the major groupings. The White category extends beyond pure snow-white to creamy tones, ivory, gray-white, and even the palest hint of mint green or lavender.
The Yellows and Oranges cover a brilliant spectrum from light tones like lemon and buttercup to deep, rich shades such as goldenrod, tangerine, and burnt orange. Breeders have achieved complex hues like salmon, coral, and rust within the orange family, which often appear to shift color depending on the light. These warm colors owe their intensity to a separate class of pigments than the reds and purples.
The cooler color families are equally diverse, encompassing Pinks, Reds, and Purples. Pinks range from delicate blush to vibrant magenta, while Reds span from bright scarlet to the nearly black tones of deep burgundy and mahogany. These “black” dahlias are not truly black but possess such a high concentration of dark red and purple pigments that they absorb almost all light.
Adding to the complexity are varieties classified as Blends, Bicolors, and Variegated, which display multiple colors on a single flower. Bicolors feature two distinct, separate colors, such as a white tip on a red petal. Variegated dahlias have contrasting colors appearing as streaks, flecks, or dots across the petals. Flame Blends typically combine yellows and oranges with vivid reds to create a fiery, multi-toned appearance.
The Missing Color and Biological Limits
Despite the dahlia’s expansive palette, one major color is naturally absent from the species: true, stable blue. The closest available colors are classified as Lavender or Mauve, which are shades of purple that can sometimes appear slightly blue in certain lighting conditions.
The reason for this limitation lies in the flower’s genetic makeup, specifically its inability to produce a particular enzyme. Dahlias naturally lack the gene for flavonoid 3′,5′-hydroxylase (F3′5′H), an enzyme necessary to synthesize the anthocyanin called delphinidin. Delphinidin is the primary precursor pigment responsible for creating blue and mauve hues in other flowers like delphiniums and cornflowers.
Without the F3′5′H enzyme, the dahlia’s biosynthetic pathway is blocked from creating the foundational structure needed for a true blue pigment. Furthermore, achieving a vibrant blue requires precise conditions, including a high pH level in the petal cell sap to stabilize the color.
The Science Behind Dahlia Pigmentation
The vast spectrum of dahlia color results from two primary families of chemical compounds: anthocyanins and carotenoids. Anthocyanins are water-soluble flavonoid pigments responsible for the reds, pinks, purples, and near-black shades. The specific hue produced is heavily influenced by the acidity (pH) of the cell sap within the petals, as well as its interaction with colorless molecules called co-pigments.
Carotenoids, which are fat-soluble pigments, are responsible for all the yellow and orange coloration. These pigments reflect light in the yellow-to-red range and are distinct from the anthocyanins. The combination of the two pigment types can produce complex bronze, peach, and flame-blended hues, determined by the concentration of each compound.
Genetic variation dictates the presence, concentration, and spatial distribution of these pigments throughout the petal. For instance, the very dark, near-black dahlias achieve their color by accumulating exceptionally high levels of anthocyanins, often by regulating or suppressing the production of competing compounds.