In the floral design world, nothing is impossible. The more unusual the elements, the more original the design. Even fruits and vegetables have been incorporated into arrangements, giving it an earthy appeal. Herbs like lavender, sage, foxglove, St. John’s wort (hypericum), and seeded eucalyptus make unique cut flowers.
Eucalyptus is native to Australia and Tasmania and belongs to the myrtle family. The name is derived from the greek word “eucalyptos,” which means well-covered. Australian aborigines used the plant as a remedy for fevers, wounds, coughs, asthma, and joint pain. The fragrant oil contained in the leaves have beneficial properties: antiseptic, anti-inflammatory, antibacterial and expectorant.
An interesting historical event took place in the mid 1800s. In Algiers, France a German botanist named Baron Ferdinand von Miller discovered that eucalyptus could be used as disinfectant in fever districts. The seeds were sent to Algiers and planted in the marshy regions. The plants thrived and converted the area into a dry and healthy environment, and as a result drove away mosquitoes and prevented the malaria disease from spreading fevers.
There are many types of eucalyptus, but the most popular in floral design are seeded eucalyptus, baby blue, and silver dollar. It is mainly used as a filler in arrangements and bouquets. Eucalyptus can also be dried and preserved as potpourri.

Types of Eucalyptus (source: http://somethingturquoise.com/2015/06/04/wedding-styling-with-eucalyptus/)