Floss Flower, a birthday flower of May 10th

Floss Flower, scientific name Ageratum houstonianum, Japanese name Ageratum アゲラタム, is one of the birthday flowers of May 10th annually. As you can see, the Japanese name comes directly from the scientific name. It means "ageless", a nod to the flower's abiliity to hold its color for an impressively long time. 

It is a soft, cloud-like bloom with a gentle texture and long flowering season. It comes in shades of blue, purple, pink and white. In Japan, Floss Flowers typically bloom from early summer through autumn, thriving in warm weather and offering steady color in gardens and parks. In the "Hanakotoba", language of flowers, floss flowers carries meanings such as "trust" and "reliability". Again, associated with the long flowering season and dependable nature of the flower. 

It is native to central America. I don't know when it was brought to Japan, but it is particularly popular in hanachozu (floating flower) displays in recent years. It is also often used in public flowerbeds because it stays neat and doesn't need a lot of maintenance. Apart from May 10th, it is also the birthday flower of September 14th, October 24th and October 29th.