The Formosa tree is a colloquial name for the mimosa (Albizia julibrissin). The tree is native to Asia and can reach 35 feet in height with a 50-foot spread. The trees have a life expectancy of 25 to 30 years, and many consider it a weed tree. They grow well in dry soil and provide a quick shade.
Mimosas form large, pink powder-puff blossoms in midsummer and bean-like seed pods, like other members of the legume family. The seeds have a hard coating that allows them to lie dormant for five or more years before sprouting to form a new tree. The trees are well-adapted to the southern United States, and there are usually numerous seedlings near the mature tree. They have compound leaves that have many leaflets, which close in the cool of the night.
While the year typically used to mark the introduction of the mimosa to the United States is 1745, it seems suspect according to the University of Arkansas Division of Agriculture. However, Thomas Jefferson included the trees in his gardens at Monticello, though there is a possibility that he obtained the seeds while serving as ambassador to France in the 1780s.
Mimosas often branch near the ground, but the crowns of the branches are weak and prone to splitting. The tree is susceptible to disease and mimosa web worms.