Cardamine hirsuta (Hairy Bitter-cress)

Native. Sx: almost ubiquitous. Arable; waste ground; walls and pavements; verges. A common weed of dry habitats, and especially frequent in urban locations. It has increased since recording for Hall (1980).

Source: C. hirsuta L. (Hairy Bitter-cress), The Flora of Sussex (2018)

Following on from last week’s cabbage, brassica or crucifer (all synonyms for what is now called Brassicaceae), this week’s #SxPOTW is another with small white flowers found on pavements, walls, waste ground and arable land. It is, perhaps, one of the quintessential ‘weeds’: those plants whose familiarity and ubiquity confer contempt or indifference. Yet this too is a native plant, with a venerable history of growth and reproduction over the millennia since the ice sheets retreated, long before humans arrived to build pavements and ignore it.

I always found its name something of a misnomer, especially as the similar and closely related Cardamine flexuosa (Wavy Bitter-cress) is considerably more hirsute. In fact Hairy Bitter-cress is not very hairy at all, with some field guides beginning their description with “Glabrous annual…”. The Cardamine part is from old mister Dioscorides (again), kárdamo being the Greek word for ‘cress’.

In most keys it is separated from C. flexuosa by the number of stamens commonly found in the flowers: four (usually) in C. hirsuta and six in C. flexuosa. I had a real problem remembering which way around the stamens were allocated, until I hit on the trick borne out of some descriptions that remind you that in C. flexuosa you have to look carefully as two of the stamens are usually shorter than the other four: close inspection will reveal them waving up at you from the bottom of the flower.

There are other means of telling the species apart, and I’d be re-inventing the wheel if I didn’t just point you at Dr Tim Rich’s YouTube video covering the differences between the commonly encountered Bitter-cresses. (There are more than two!) However, key features are the strong basal rosette of leaves and the few (zero to three or four) stem leaves.

As our entry in the Flora tells you, C. flexuosa tends to prefer damper habitats, such as streamsides and woodland. Its distribution shows a pattern of absence over the drier chalk downland.

Native. Sx: very common. Damp woodland; streamsides; damp shady grassland. It is also found occasionally as an urban weed but less frequently than C. hirsuta. W-Dod (1937) notes that in the past it had been confused with C. hirsuta.

Source: C. flexuosa With. (Wavy Bitter-cress), The Flora of Sussex (2018)

Pagans may know the plant by the Anglo-Saxon name stune, one of the nine herbs of the Nine Herbs Charm. So far as I know, this has yet to be tested against Covid-19.

People might ask why not choose C. pratensis (Cuckoo Flower or Lady’s Smock) over C. hirsuta as this week’s plant: it’s coming into flower around now and is certainly more attractive. But we love all plants here at the Sussex Botanical Recording Society, not just the fancy ones. Someone has to stand up for the overlooked, unappreciated and literally downtrodden!