The Ipomoea genus, commonly known as Morning Glory, encompasses fast-growing, twining vines recognized for their striking, trumpet-shaped flowers. These ornamental plants are distinctive because their blooms follow a daily cycle, typically opening in the early sunlight and closing by the afternoon heat. The diversity of their brilliant coloration has made Morning Glories a popular garden choice across many different climates.
The Full Spectrum of Morning Glory Colors
Morning Glories display a color palette encompassing nearly every shade except pure yellow or green. The most sought-after colors are the deep blues and purples, exemplified by the classic ‘Heavenly Blue’ cultivar, which features a vivid sky-blue petal with a contrasting white and yellow throat. Many varieties of the common Morning Glory (Ipomoea purpurea) produce deep violet and magenta blooms.
Pinks and reds are common in other popular varieties, such as the ‘Crimson Rambler’, which offers striking red trumpet-shaped flowers. White varieties, like ‘Pearly Gates’, offer a simple, clean contrast to the more intensely colored flowers. Bi-colored and multi-streaked cultivars also exist, such as ‘Flying Saucers’, which display intricate patterns of blue, white, and purple streaks across a single bloom.
Why Morning Glories Have Color
The vibrant colors of Morning Glory flowers originate from a class of pigments called anthocyanins, which are water-soluble compounds stored within the plant cell’s large central vacuole. These flavonoids are responsible for most red, purple, and blue colors found in the plant kingdom. The specific color hue produced is determined by the chemical structure of the anthocyanin molecule itself.
Morning Glories produce various anthocyanidin cores, such as cyanidin, which tends to yield purple and blue shades, and pelargonidin, which underlies pink and reddish colors. The particular shade is further modulated by the attachment of sugar molecules and organic acids, which stabilize the pigment. Co-pigments, like flavones, also interact with the anthocyanins to intensify or slightly shift the final visible color.
How Environment Influences Flower Hue
While the type of anthocyanin produced is dictated by the plant’s genetics, the final flower color is sensitive to the environment within the petal cell. The most significant cellular factor is the vacuolar pH (pHv), the acidity or alkalinity of the liquid where the anthocyanins are dissolved. Anthocyanins function like natural pH indicators, shifting their color depending on the surrounding acidity.
In the ‘Heavenly Blue’ cultivar, the petals are purplish-red when the flower is in the bud stage because the vacuolar pH is mildly acidic, around 6.6. As the flower opens fully, a specialized tonoplast-localized protein, the Na+/H+ exchanger (NHX1), becomes highly active. This protein actively transports ions, such as potassium, into the vacuole while pushing hydrogen ions (protons) out.
This ion exchange causes the internal pH to increase dramatically to a weakly alkaline 7.7. This shift changes the anthocyanin structure, instantly transforming the color from purplish-red to sky-blue. Environmental factors like the availability of soil minerals, particularly potassium, can influence the efficiency of this ion exchange mechanism, affecting the clarity and depth of the blue hue.