Hairy Bitter Cress

Hairy Bitter Cress has a sister plant called Wavy Bitter Cress (Cardamine flexuosa), which I wrote about here. The most important distinguishing features, at least that I can make out, are firstly that Wavy has six stamens and Hairy has four, and secondly that the seed pods of Wavy only grow up to the height of the flowers whereas those of Hairy grow beyond as shown in the photo below.

Hairy Bitter Cress
(Cardamine hirsuta)

The flowers are tiny and always seems to be closed when I come across the plants so determining the number of stamens is a fiddlesome job with fine tweezers under a microscope.

The fruit pedicels of Hairy grow beyond the flowers in part, I think, because they are erect, relatively speaking, whereas they are more spreading in Wavy. The stems of Hairy are straight, relatively speaking too, whereas wavy gets its name from its more wavy stems.

C. hirsuta erect seed pods
and relatively straight stem

In the Boggy Brae garden I found Wavy on April 21 and Hairy just today, May 19.

Hairy Bitter Cress is boggybrae wild plant no.54 for 2015.

Wavy Bitter Cress (Cardamine flexuosa)

Quick edit... probably my best pic of Wavy, showing the "oh so flexuoso" stems: