Plants are classified into groups based on their common characteristics, such as leaf arrangement and the structure of their fruit and flowers. People generally call flowers by their common names, such as "daisy," but in fact, many different flowers belong to the daisy family, including sunflowers, asters, and what we normally think of as daisies. That's why botanical names are so important.
The first part of a flower's three-part botanical name is the "family" name. Plants are classified as belonging to a certain family on the basis of similar characteristics, primarily fruit and flowers. Often the family name ends with the letters "aceae," Latin for "belonging to, having the nature of." The family name for all the various types of daisies, for example, is Asteraceae.
Genus is the next category, similar to a surname. Plants within the same genus are structurally similar. It's still a fairly broad grouping that is divided further by the next category, species. The genus name is listed before the species name, similar to the manner of alphabetizing Western names ("Smith, Jane"). Sunflowers, which as mentioned above belong to the daisy or Asteraceae family, are of the genus Helianthus.
A plant's species is like its first name, although it is listed after the genus. Unlike the genus, the species name is not capitalized. The annual sunflower's species is annus, and its genus is Helianthus. Its two-part botanical name, therefore, is Helianthus annus.
Cultivars are plants that have been deliberately produced through selective breeding. They are an offshoot of a specific species. The word cultivar comes from the term "cultivated variety." Cultivar names are listed after the species name. One cultivar bred from the sunflower is Helianthus annus "Teddy Bear," which produces an orange-yellow flower with a less distinct center than the more common sunflower varieties.
Hybrids are created by the cross-pollination of two distinct species. This process occurs naturally and when botanists choose to breed plants that way to create a plant with specific characteristics. Plants with an "x" in the middle of their name are hybrids, such as Helianthus x multiflorus, which is a combination of Helianthus annus and Helianthus decapetalus.
Some of the botanical names for flowers have special meanings. Many flowers are named for well-known scientists, such as the zinnia. The zinnia honors Johann Gottfried Zinn, a professor of botany in Göttingen, Germany, during the 1700s. Other flowers are named for mythical figures: the peony (Paeonia) is named for Paeon, the legendary Greek physician to the gods. And some flowers' botanical names simply describe their features with words from the Latin language: "alba" is white, "purpureus" is purple; "macrothyllus" means "large leaves."