There are over 20,000 different species of the family Asteraceae, which is sometimes referred to as the family of daisies. Daisies are a star-like flower, hence the name, from the Greek aster. Some members of Asteraceae, such as many lettuces and sunflowers, are not thought of as daisies, but they share many of the same characteristics.
The family Asteraceae is quite old at upwards of fifty million years in its full formation. Its plants make up nearly ten percent of all flowering plants on Earth, and it's arguable as to whether it or the orchid family holds more genera and species. Daisies include not only the blooms most people are familiar with, but also popular health herbs such as Echinacea and arnica, and many edible plants such as artichokes and endive.
When most people think of daisies, however, they think of a number of flowering plants. Though these flowers all fall within the family Asteraceae, they have little else in common to the casual observer.
The true daisy--that with which the name originated--is the English daisy, Bellis perennis. The word "daisy" is a contraction of the phrase "Day's Eye," and references the fact that English daisies close at night and open their petals again at daylight. Daisies originated in northern Europe, but spread throughout Europe and to the Americas in the 1600s. English daisies have white, off-white, or sometimes slightly pink petals and a yellow center, with green stems and leaves.
Chrysanthemums, an entire genus within Asteraceae, are the next largest group of flowers many people think of as daisies. Many Chrysanthemums appear very similar to the English daisy, with white petals and a yellow center. Others come in decorative colors, ranging from vibrant pinks and blues to deep purples and reds. The most common Chrysanthemum, grown in parts of Asia as a food crop, is Chrysanthemum coronarium; this flower, also known as the crown daisy, appears very similar to the English daisy, but with yellow petals as well as a yellow center.
While many daisies have the typical daisy appearance of star-spread petals around a central yellow area, others look entirely alien. The African daisy, for example, has bright purple petals which curl up at the ends, and a collection of blue, yellow-tipped central florets. The globe thistle, also a daisy, has no obvious ray-shaped petals, instead appearing as a ball. Many dahlias, by contrast, have the classic star configuration of petals, with none of the interior florets.
Daisies essentially come in all colors and sizes, from lavender to maroon to the purest whites. They can be found in every country on earth, growing in virtually every climate. They are easy to grow and propagate, and are suited to handle extremely dry soil, making them ideal for beginning gardeners.