The Cuckoo Flower was there two weeks ago but I didn't stop to take a close look. Last Sunday I took a photograph for two, and confirmed it was a cress of some kind.
I wasn't familiar with Cardamine pratensis but know a few of its close relatives from when I wrote up the Brassicaceae family for the Flora of Victoria. Looking through that account I see there was a single record of this species from near Ballarat in the nineteenth century.
As Brassicaceae go, the Cuckoo Flower is one of the showier species. The pale blue flowers are eye-catching by the side of the Thames tow path near Kew Gardens. It also grows within the botanic garden, but I haven't seen it there yet. The first record inside the fence was in 1873 when it was common throughout the estate but particularly between Kew Palace and the Herbarium.
The Cuckoo Flower takes its most common common-name from the (in)famous migratory bird that arrives in the UK at the same time as Cardamine pratensis flowers. Well at least this is what used to happen. I gather the cuckoo normally arrives in late April or early May whereas the Cuckoo Flower is flowering now, following the trend of most spring flowers here and opening at least a couple of weeks earlier than it was when these names were concocted.
The Virtual Hebrides site lists a few more common names. Lady's Smock is one I've seen elsewhere. According to this website the name alludes to a maid's smock, conjuring up a rather romantic association for the flowers.
It goes on to say that "when Christianity came this feminist association was attributed to the Virgin Mary - which led to the flowers also being called. my lady's smock, lady's glove". Other common names include Lucy, Shoes and Stockings, Gilliflower, Milkmaids and Apple Pie (apparently a reference to the perfume of the flowers). In Ireland the species is called Biolar gréagháin.