Chrysanthemums, belonging to the genus *Chrysanthemum* within the family Asteraceae, are one of the most diverse and complex groups of flowering plants in horticulture. From a botanical perspective, their classification can be understood through their morphological characteristics, primarily the structure of their inflorescences, which are typically composite flower heads composed of many individual florets. This diversity is largely a result of centuries of selective breeding, which has accentuated specific traits in the ray and disk florets.
Before delving into types, it is crucial to understand the basic botany of a chrysanthemum bloom. What appears to be a single flower is actually a capitulum, or a dense head, composed of two types of florets. The central part of the flower head consists of **disk florets**. These are tiny, tubular, and fertile, containing both male and female reproductive parts. Surrounding the disk florets are the **ray florets**. Each ray floret is strap-shaped and resembles what we commonly think of as a "petal." In many cultivated types, the disk florets are suppressed, and the ray florets are exaggerated, leading to the vast array of forms. The variation in the arrangement, shape, and proportion of these two floret types defines the different classes of chrysanthemums.
Botanists and horticulturists classify chrysanthemums based on the morphology of their flower heads. One major division is between **standard** and **spray** types. Standard (or disbud) types produce one large, primary flower per stem, achieved by removing the side buds. Spray types are allowed to develop multiple smaller flowers on a branching stem. Beyond this, the forms are categorized by the appearance and arrangement of the ray florets.
Irregular Incurve: These are the giant, globular blooms often seen in exhibitions. The ray florets curve inward and downward to form a dense, impenetrable-looking ball, with the lower florets hanging loosely, creating a "skirt." The center of the flower head is fully concealed.
Reflexed: The ray florets in this class curve downward and overlap in a regular, imbricated pattern, similar to the plumage of a bird. The flower head has a flat, mound-like appearance from the top.
Anemone: This form presents a clear distinction between the two floret types. The disk florets in the center are elongated and form a raised, cushion-like dome, while the ray florets form a single or double row of flat petals around the outside.
Spider: Botanically fascinating, spider chrysanthemums have ray florets that are long, tubular, and hooked or coiled at the ends. This gives the flower a spidery, intricate look, and the florets are often fine and delicate.
Pompon: These are small, spherical, button-like flowers that are perfectly globular. The ray florets are short and curve inward entirely, hiding the disk. They are typically borne in spray formations.
Single/Daisy: This form most closely resembles the wild ancestors of chrysanthemums. It features a central disc of fertile disk florets surrounded by a single, outer ring of ray florets, looking very much like a daisy.
Quill: The ray florets are straight, tubular, and hollow at the tip, resembling a quill pen. The blooms can appear spiky and textured.
From a plant science viewpoint, the incredible diversity of chrysanthemum forms is a testament to the plasticity of the Asteraceae family's floral structure. Breeders have manipulated genetic expressions to control floret development, creating forms that may reduce or eliminate the plant's ability to reproduce sexually (e.g., double-flowered types with no disk florets) in favor of aesthetic appeal. This makes the cultivated chrysanthemum a prime example of the interplay between natural botanical potential and human-driven artificial selection.
