ageratum

noun

1. any of several composite plants of the genus Ageratum, especially A. houstonianum, having heart-shaped leaves and small, dense, blue, lavender, or white flower heads, often grown in gardens.
2. any of various other composite plants, as the mistflower, having blue or white flowers.

noun

1. any tropical American plant of the genus Ageratum, such as A. houstonianum and A. conyzoides, which have thick clusters of purplish-blue flowers