Ageratum with a Verbenum behind, in the backyard.
Ageratum, known as Whiteweed, is a genus of 40 to 60 tropical American herbs, annuals and perennials from the Sunflower family Asteraceae, tribe Eupatorieae. The fluffy flowers are lavender-blue, pink, lilac, or white; and spread in small compound umbels. Most species are native to Central America and Mexico but four are native to the United States. (Wikipedia)