This is the flower of a Common Hemp-Nettle. The scientific name of this plant is Galeopsis tetrahit.

It can be hard to distinguish Galeopsis tetrahit from Galeopsis bifida, which is a close relative. These two species also occasionally crosspollinate to create hybrids making the situation even more complex. When trying to determine if a particular specimen is Galeopsis tetrahit or Galeopsis bifida, one will usually look for three particular characteristics of the middle petal amongst the three lower ones, plus one other characteristic. The characteristics are:

• The darker region does not extend all the way to the boundy of the petal middle lower petal.
• The middle lower petal does not have a dent or a cleavage in it.
• The middle lower petal is square-like.
• The hairs on the upper half of the stamen got little glands at the top.

The particular specimen in this image exhibits all four of these typical characteristics of Galeopsis tetrahit (to bad the technical merits of the photo isn't as perfect).

An older but synonymuous scientific name is Galeopsis carthusianorum.

Camera: Nikon D50 with a 18-55mm lens

Location: In the parkish forest area behind the botanical garden of Gothenburg, Sweden.