Pennyroyal

My initial impression on finding Pennyroyal (Mentha pulegium) was, "bottle brush." These odd looking plants have blue-purple bristle-like flowers arranged in small tufts, up and down the stem. They are fairly short, about 10 inches tall at most, but they grow in clusters as seen below. Pennyroyal is native to Europe and was introduced for culinary and medicinal purposes. However, as with many introduced species, it has become a weedy pest in Northwest gardens.

Pennyroyal is a member of the Mint (Mentha) genus and as such has a strong spearmint aroma. On the downside though, it also contains pulegone, which is poisonous to humans! Nevertheless, Pennyroyal has a rich past of herbal uses. It has been used in aromatherapy and other culinary applications. Today it is mainly used in dried floral arrangements. The aroma is thought to repel fleas and mosquitoes. For more details, see: http://en.wikipedia.org/wiki/Mentha_pulegium.

Pennyroyal seems to prefer marsh areas or other seasonally wet, disturbed areas. We found these growing along the service road at Jackson Bottom Wetlands (7/30/2013).

Note the bumblebee for size. 

Most were growing in clumps like this one.

Detail of tiny blossoms.