The tulip is a perennial, bulbous plant with showy flowers in the genus Tulipa, of which up to 109 species[1] have been described and which belongs to the family Liliaceae. Tulips are spring-blooming perennials that grow from bulbs. Depending on the species, tulip plants can grow as short as 4 inches (10 cm) or as high as 28 inches (71 cm). Tulip stems have few leaves, with larger species tending to have multiple leaves. Plants typically have 2 to 6 leaves, with some species having up to 12. Tulips are indigenous to mountainous areas with temperate climates and need a period of cool dormancy, known as vernalization. They thrive in climates with long, cool springs and dry summers. Although perennials, tulip bulbs are often imported to warm-winter areas of the world from cold-winter areas, and are planted in the fall to be treated as annuals. Tulip bulbs are typically planted around late summer and fall, in well-drained soils, normally from 4 to 8 inches (10 to 20 cm) deep, depending on the type planted. Carolus Clusius planted tulips at the Imperial Botanical Gardens of Vienna in 1573 and later at the Leiden University's newly established Hortus Botanicus, where he was appointed director. There he planted some of his tulip bulbs in late 1593. As a result, 1594 is considered the official date of the tulip's first flowering in the Netherlands, despite reports of the flowers being cultivated in private gardens in Antwerp and Amsterdam two or three decades earlier. These tulips at Leiden would eventually lead to both Tulip mania and the commercial tulip Regardless of how the flower originally arrived in Europe, its popularity soared quickly. Carolus Clusius is largely responsible for the spread of tulip bulbs in the final years of the sixteenth century. He finished writing the first major work on tulips in 1592, and he made note of the variations in colour that help make the tulip so admired. While occupying a chair as a faculty member in the school of medicine at the University of Leiden, Clusius planted both a teaching garden and private plot of his own with tulip bulbs. In 1596 and 1598, Clusius suffered thefts from his garden, with over a hundred bulbs stolen in a single raid. Between 1634 and 1637, the early enthusiasm for the new flowers triggered a speculative frenzy now known as the tulip mania. Tulips would become so expensive that they were treated as a form of currency. Around this time, the ceramic tulipiere was devised for the display of cut flowers stem by stem (bouquets displayed in vases were rare until the 19th century, although such vases and bouquets, usually including tulips, often appeared in Dutch still-life painting). To this day, tulips are associated with the Netherlands, and the cultivated forms of the tulip are often called "Dutch tulips."