Bittercresses for beginners

by David Bevan

The bittercresses (Cardamine) can be a confusing group to get to know as several of them bear rather similar small white flowers. But each individual flower is very beautiful when examined under a hand lens! They are also some of the first plants to flower in the spring and they include some handsome garden relatives.

Bittercresses are in the cabbage (or cress) family which was, until recently, known as the Cruciferae. This useful name is derived from the Latin word "crux", meaning a cross, and refers to the “cross-shaped” arrangement of the four petals in each flower. The family name now in favour is the rather less appealing Brassicaceae. The shape and size of the fruits is of critical importance in naming members of the cabbage family. In the bittercresses, the fruits (seed pods) are all long and thin. A useful feature of all bittercresses is that they generally have pinnate or ladder-like leaves with the side leaves (known as leaflets) on a distinct stalk (see photo opposite).

Cardamine pratensis (Lady's Smock)

The large pink flowers of Cardamine pratensis (Lady's-smock) taken near Hatchmere, Cheshire 17 05 04.

C. hirsuta (Hairy bittercress) and C. flexuosa (Wavy Bittercress) may look similar with small white flowers and a cress-like smell if you crush the leaves. The key difference to remember is that usually Hairy Bittercress is not very hairy (usually only along the leaf edges) and that it has 4 stamens. Wavy bittercress has 6 stamens. A way of remembering this is flex = sex (Latin for 6) = six. Careful though, the 2 outer stamens may be shorter and overlooked. Wavy bittercress normally prefers a damper habitat by streams and ditches whereas hairy bittercress usually grows in drier, weedy places and on wall tops. However, these habitat preferences are not absolute and wavy bittercress, for example, can sometimes be found in quite dry places. If touched when ripe, the pods curl up and spring open, scattering the seeds a considerable distance. Hence another common name for hairy bittercress is "popping cress".

Two less common bittercresses are C. amara (large bittercress) and C. impatiens (Narrow-leaved Bittercress). Large Bittercress is similar to Lady’s-smock but usually has white flowers and always has violet anthers.

Cardamine amara (Large Bittercress)

The white flowers of Cardamine amara (Large Bittercress) are slightly smaller than C. pratensis (Lady's Smock) and have violet anthers.

C. amara (Illustration 5) has a more restricted distribution and prefers wetter acid soils. Narrow-leaved bittercress has distinct auricles (pointed ear-like lobes at the base of the leaves - (see the illustration below Cardamine bulbifera opposite). It grows in woodland (especially under ash) in the Southeast and on limestone in North Somerset, Wales, the Peak District and the Pennines.

Bittercress Hybrids

Bittercress hybrids are rare and often difficult to identify. However one rather striking example came to light at Bentley Priory in the West London borough of Harrow. The grassland here is cattle-grazed and particularly rich in wild flowers. There are extensive populations of both Lady’s-smock and Wavy Bittercress in the wetter areas. In April 1989, while taking a party of students to explore the flora, my eye was caught by a large patch of an unusual white-flowered bittercress growing under a willow tree in a damp hollow. A rather fierce-looking bullock prevented immediate closer examination and I was forced to return later. The flowers were pure white, produced very profusely and, with individual plants covering an area of some five square metres, they made a fine display. I suspected that they might have been hybrids as the flower size was intermediate between the larger ones of lady’s-smock and the tiny ones of wavy bittercress. However, flower size can be very variable in lady’s-smock and 1 was far from certain.

There was only one thing to do — talk to Tim Rich! Tim knows more about Crucifers than almost anybody, having written the splendid BSBI handbook on the family. Within a few days he was on site and “throwing down the gauntlet”! If the plants were indeed of hybrid origin, as he also now suspected, it should be possible to “recreate” them by deliberately cross-pollinating between neighbouring plants of the two suspected parents. I set about doing just that, cross pollinating between a whole range of different individual plants of Lady’s-smock and wavy bittercress. I then grew on resulting seeds.

To cut a very long story short, I ended up with four seedlings — all derived from crosses involving a white-flowered form of lady’s-smock. Three were eaten by slugs, but the fourth produced flowers identical to those of the original mystery plant. Honour had been satisfied and the hybrid origin of the Bentley Priory bittercress had been proved to Tim's satisfaction! It was the first time it had been found in Middlesex. I stumbled on it again while recording for the Flora of Ashdown Forest - but that is another story!

Cardamine sp (A Bittercress)

A rosette of a Cardamine showing pinnate, stalked side leaflets. Photo taken in Cheshire 17 01 06.

The three most common are lady’s-smock or cuckoo flower, hairy bittercress and wavy bittercress. Cardamine pratensis (Lady’s-smock) is a common plant of damp grassy places. It has comparatively large pink flowers (occasionally white) and yellow anthers. It is apparently resistant to some herbicides and can often be found growing on wet lawns — at Compton in Surrey sheets of lady’s-smock cover the (rather boggy) recreation pitch each spring. Pretty double flowered forms occur occasionally.

Cardamine flexuosa (Wavy Bittercress)

Flowers of Cardamine flexuosa above showing the long fruits, small white flowers and tiny yellow anthers which can be counted using a hand lens.

Cardamine hirsuta (Hairy Bittercress)

Flowers of Cardamine hirsuta above showing how similar the flowers and friuts are to C. flexuosa. There are only four anthers on this plant.

The rarest native bittercress is C. bulbifera (Coral-root). This plant has flowers about the same size as lady’s-smock but of a deeper shade of pink. The most striking feature however is the presence of small, rounded, purple-brown or black bulbils in the axils of many of the leaves. These are reproductive structures which can give rise to new plants. They are diagnostic of coral-root which grows in dry woods on chalk in the Chilterns and in wet woods on clay in a few places in the Weald.

Cardamine bulbifera (Coralroot)

Cardamine bulbifera: one of the UK's rare plants after flowering. The fruits are the rather insiginificant pods at the end of the stalk but the purple "grapes" are bulbils which can fall off and grow into new plants. Photo taken on WFS North Yorkshire meeting; Scalby 21 06 05.

Illustration 1 (Above)

An illustration of the leaves of Cardamine impatiens ( Narrow-leaved Bittercress) showing the auricles.

Cardamine raphanifolia (Greater Cuckoo Flower)

Not a hybrid but an unusual introduction from Southern Europe which looks a bit like a deep coloured Cardamine pratensis (Lady's Smock or Cuckoo Flower). The leaves are different and it is only found scattered over Britain where it has escaped from cultivation.