The National Chrysanthemum Society separates the varieties of chrysanthemum into 13 different classes: irregular incurve, reflex, regular incurve, decorative, intermediate incurve, pompon, single and semi-double, anemone, spoon, quill, spider, brush or thistle, and unclassified or exotic. Within these classifications, there are about 40 generally recognized species and thousands of varieties.
Chrysanthemum blooms are made up of many individual flowers called "florets," each one capable of producing a seed. Disk florets are clustered in the center of the bloom. Ray florets are arranged around the perimeter. Thousands of years of selective breeding has led to remarkable variation in size and appearance. Irregular incurves have been bred to produce a giant, rounded head of curving florets. Regular incurves produce a smaller, denser globe.
The florets on the reflex form fall outward to give the flower a mop-like appearance. Anemones have prominent ray florets arranged around a mounded center. Spider varieties have tube-like ray florets with barbed ends that hang down around the stem. Chrysanthemum enthusiasts often classify different types as hardy or decorative. All are herbaceous perennials, preferring full sun and well-drained soil. Chrysanthemums bloom in response to seasonal changes in daylight, so planting near artificial lighting can wreak havoc with their natural blooming cycle.