Like most flowers, tulips come in many varieties. However, among those varieties larger categories exist that tulips are grouped into. The larger categories define things like the size, blossom type and growing time of the tulip. Individual varieties within a category vary more in terms of color or the specific appearance of the bloom.
Single tulips are be divided by the time of year that they bloom in. The average single early tulip grows to a height of 10 to 18 inches and blooms in the early spring. Single late tulips grow at the end of the spring and are usually the last tulips to bloom. Late varieties tend to grow taller, averaging 18 to 30 inches. They are called "singles" because they have the typical six-petal configuration of tulips.
Several categories of tulip bloom around the end of April and are thus considered a midseason flowers. Darwin and Triumph tulips both bloom around this time. Triumphs combine characteristics from other types of single tulips but bloom in midseason and are prized for their variety of colors. Darwins can grow as tall as 30 inches. Wedding bouquets that feature tulips often use Darwins because of their long stems.
Several types of tulip fall into nontypical categories. They have flower shapes that are different from the cup shape common on single tulips. Lily, fringed and parrot tulips all have abnormal flower shapes. Parrots exhibit twisting and curling in the petals. Lily tulips, unsurprisingly, look more like a lily, with petals that extend away from the center. Fringed tulips have delicate lacy edges on each petal.
Double tulips have extra petals. The extra petals make them resemble other varieties of flowers more than single tulips. Double late tulips are even sometimes called "peony" tulips. Like the regular single varieties, late and early varieties of double tulips exist. The blossom of the double late flower grows as large as 6 inches across. Double early and late tulips bloom at the corresponding time of their single flower counterparts.