From a botanical perspective, the diverse colors of chrysanthemums (Chrysanthemum spp.) are not symbolic but are the result of complex biochemical and genetic factors. The pigments responsible for their vibrant hues are primarily flavonoids (anthocyanins for reds, purples, and blues), carotenoids (for yellows, oranges, and reds), and chlorophyll (for greens). The specific color expressed in each bloom is determined by the unique combination and concentration of these pigments, which is in turn controlled by the plant's genetics and influenced by environmental conditions such as soil pH, light exposure, and temperature.
Botanically, white chrysanthemums are characterized by a near-complete absence of anthocyanin and carotenoid pigments in their ray florets (the "petals"). Instead, they appear white due to the reflection of all visible light wavelengths. The cells in the florets contain air spaces that scatter light, much like how snow appears white. From a plant's viewpoint, this high reflectivity can potentially aid in protecting the reproductive organs in the flower's center from excessive solar radiation and heat. The green center, or disc floret, remains rich in chlorophyll, highlighting its role in photosynthesis even during flowering.
The bright yellow and orange shades are predominantly due to the presence of carotenoid pigments, such as beta-carotene. These lipid-soluble pigments are synthesized and stored within specialized plastids called chromoplasts inside the cells of the ray florets. Carotenoids play a crucial biological role beyond coloration; they act as accessory pigments in photosynthesis, helping to absorb light energy and dissipate excess energy to prevent damage to the plant's cells. The variation from pale lemon to deep gold is a direct result of the specific type and density of carotenoids present.
The deep red, pink, and purple colors are engineered by anthocyanin pigments. These water-soluble pigments are stored in the vacuoles of the plant cells. The exact hue—whether crimson, magenta, or lavender—is highly sensitive to the pH of the cell sap. A more acidic vacuolar environment will tend to produce redder tones, while a more neutral or alkaline environment can shift the color toward purple or even blue, though true blue is rare in chrysanthemums due to their specific genetic makeup. Anthocyanins also serve a protective function for the plant, acting as a "sunscreen" to shield sensitive tissues from high-light stress and potential damage from UV radiation.
Green-flowered cultivars are a fascinating botanical example of a homeotic mutation, where the development of one part of the plant is altered. In these chrysanthemums, the ray florets (typically non-photosynthetic petals) retain chloroplasts and chlorophyll, the pigments responsible for photosynthesis in leaves. This means these specialized "petals" remain partially vegetative and capable of producing sugars for the plant, blurring the line between a petal and a leaf. This unique trait is a result of selective breeding that has suppressed the genes that usually cause the loss of chlorophyll in the florets.
