As I walk down the marshy trail there is a strong minty smell in the air. This is coming from small purple-flowered plants: pennyroyal, or Mentha pulegium is in the mint family and almost always grows in wetlands. Even if the ground appears dry, it’s a strong indicator that a low summer-dried fields or valleys was wet in the spring, according to the Flora of Marin. Pennyroyal is another weedy non-native species native to Ireland and other parts of Europe.
There are a lot of other members of the mint family that have tuft-like purple flowers, but pennyroyal is the only one in the area that has discrete whorls of leafless (or small-leaved) flowers in stacks along the stem.
Flowers Of Marin 