Chrysanthemums, often called mums, are widely cultivated ornamental plants prized for their spectacular late-season blooms. These members of the Asteraceae family originated in East Asia, with a long history of cultivation beginning in China as far back as the 15th century B.C. Over millennia, breeding has transformed the mum into thousands of diverse cultivars, each possessing a unique visual profile of shape, texture, and color.
Defining Characteristics of the Chrysanthemum Flower
The structure recognized as a single chrysanthemum flower is botanically a composite inflorescence called a capitulum, or flower head. This head is a dense cluster of many tiny individual flowers, referred to as florets. The capitulum’s architecture is divided into two distinct types of florets that determine the bloom’s overall appearance.
The center of the flower head is composed of disc florets, which are small, tubular, and usually yellow. These disc florets are considered perfect flowers, possessing both male and female reproductive organs. Surrounding the central disc are the ray florets, which are the elongated, petal-like structures that provide the flower’s size and dramatic coloring.
Ray florets generally possess only female reproductive organs. The vast variety seen across chrysanthemum types results from genetic variations that alter the shape, length, and quantity of these outer ray florets.
The Diverse Spectrum of Mum Flower Forms
Chrysanthemum classification is based on the morphology of the ray florets, resulting in numerous distinct flower forms.
- Incurved types have ray florets that curve upward and inward, creating a dense, symmetrical, globe-like bloom that often conceals the central disc.
- Reflexed mums feature ray florets that curve downward and outward, giving the flower a flattened, skirted appearance.
- Pompon forms produce a small, firm, spherical bloom composed of many tightly packed, short ray florets.
- Spider chrysanthemums are characterized by long, slender ray florets that are often tubular and may curl or twist, creating a delicate, spidery texture.
- The Quill form is defined by narrow, straight ray florets that resemble tiny tubes radiating outward.
- Spoon chrysanthemums have spatulate ray florets where the lower portion is tubular, but the tip opens into a distinct, spoon-like shape.
Color Variation and Pigmentation
The chrysanthemum’s expansive color palette results from complex biochemical pathways involving several pigment groups. Yellow and orange hues are created by carotenoids, which are lipid-soluble pigments stored within cell structures. The concentration and type of carotenoid directly influence the shade, ranging from pale lemon to deep gold.
The pink, red, and purple colors are derived from anthocyanins, a class of water-soluble flavonoid compounds. A lack of these pigments entirely results in a white flower, as the color is determined by the reflection of light off the cell structure. Breeding efforts have successfully combined these pigment types, leading to complex colors like bronze, dark red, and purplish-red.
The intensity of a mum’s color depends on the accumulation level of these pigments. Breeders have utilized modern genetic techniques to introduce novel colors, such as blue/violet shades, which were not traditionally present in the species. This biological diversity ensures the chrysanthemum can provide virtually every color except a true blue.
Growth Habits and Plant Structure
The chrysanthemum plant’s structure is defined by its foliage and growth habit. The leaves are typically dark blue-green, deeply lobed, and slightly aromatic. They are arranged alternately along the stem, contributing to the plant’s dense appearance.
Mums exhibit a herbaceous perennial growth habit, forming vigorous, clump-type plants with strong stems. Cultivars range significantly in height, from compact types under 12 inches to taller varieties reaching up to 36 inches. Garden mums naturally have a mounding or bushy form, often enhanced by “pinching” the stems to encourage lateral branching.
The timing of the floral display is a defining characteristic, as the mum is a short-day plant. Flower bud formation is triggered by the shortening day length of late summer and early fall. This results in the characteristic bloom from September until the first hard frost, ensuring the mum is a visual anchor in the garden when most other plants have finished their bloom cycle.