Cardamine pratensis L., Cuckooflower

Account Summary

Growth form and preferred habitats

A semi-rosette perennial, with pinnate leaves, shallow rooting and possessing a short horizontal rhizome which overwinters with a tiny, almost insignificant leaf rosette (Grime et al. 1988), C. pratensis is most frequent and locally abundant in damp to wet, open (ie well-illuminated) water meadows (ie seasonally flooded ground) − of which around its lakes, Fermanagh has very many hectares, plus other forms of more or less damp pasture and grassy roadside verges. The species can also be found much less frequently and growing very much more sparsely in shaded situations in drier sites, eg on wood margins or in clearings, on hedgerows, as well as in wetter lakeside fens and marshy ground by streams and rivers. It also occurs thinly scattered in upland rushy pastures and, again, in wet or damp flushes to a limited extent, but it is never found on steep slopes or on shallow, rocky ground. Neither would one find it in permanently wet ground.

C. pratensis is a plant closely associated with ± closed grassy turf rather than with bare or heavily disturbed ground, but obviously its seed (or plantlets − see below), must colonise gaps in the vegetation cover. Like the majority of small or less sturdy plants (with which it would definitely be grouped), Cuckooflower is only weakly competitive and cannot invade and establish itself among tall, rank, heavily shading and vigorously competing species in any form of vegetation. However, it can colonise and become established when the environment is modified and plant competition limited by factors which restrict dominance, including regular grazing, cutting, or moderate levels of other forms of disturbance (Grime et al. 1988; Rich 1991).

It seems to prefer moderately acid to neutral soil reaction (pH 5.0-7.5) and performs best in moderately fertile soils, although it is also found in calcareous, base-rich sites. Due to excessive amounts of calcium ion, these soils are generally mineral-poor or unbalanced for the plants' nutrient requirements and are thus best considered nutrient-poor (Dale & Elkington 1974; Grime et al. 1988).

Fermanagh occurrence

Cuckooflower (or Lady's Smock) is one of the most familiar, widespread and welcome spring flowers to Fermanagh residents, with whole fields being coloured by its charming, soft lilac blossom in early May.

C. pratensis is in fact by far the most commonly recorded member of the Brassicaceae (Cruciferae) in the Fermanagh Flora Database. There are a huge number of records from 405 tetrads, 76.7% of those in the VC. C. pratensis is well over twice as frequent and three times as widespread as the second ranking species in the family, Rorippa amphibia (Great Yellow-cress).

Genetic variation

The flower colour of C. pratensis is easily observed to vary from a delicate lilac-mauve to pure white, but in both genetic terms and in chromosome complement, the plant variation is so great that the species really comprises a species aggregate or complex, involving a wide spectrum of chromosome numbers from 2n=16-84, plus aneuploids and hybrid forms involving aneuploids (Hussein 1955; Allen 1981). Studies in a wide range of habitats in C & N England found that almost all C. pratensis populations were of the same chromosome complement (2n=56) (Dale & Elkington 1974). This study showed there was wide variation in numerous floral and vegetative characters and transplant experiments proved that much of the variability was environmentally governed (ie the plants were phenotypically very plastic). This work also showed that the form recognised as C. palustris (Wimmer & Grab.) Peterm. in lowland NW Europe, does not fit English material and, consequently, in his BSBI Handbook, Crucifers of Great Britain and Ireland, Rich (1991, p. 144) decided it was best to treat C. pratensis as a single polymorphic species until such time as its taxonomy had been further studied.

Flowering reproduction

The pretty flowers of Cuckooflower are insect pollinated and show a high degree of self-incompatibility, but it is not absolute (Salisbury 1965). The incompatibility mechanism is of the 'di-allelic sprophytic type', similar to the genetic control of 'pin' and 'thrum' heterostyly in the genus Primula (Richards 1997a, p. 206). Multi-allelic sporophytic incompatibility systems appear to be largely (but again, not entirely) confined to two large plant families, the Brassicaceae (or Cruciferae) and the Asteraceae (or Compositae).

While C. pratensis is extremely variable in numbers of flowers and their size and form, it has a surprisingly low seed output. This is due to a combination of factors amongst which soil moisture level, severity of competition and the intrinsic self-incompatibility, rank as most important. In a closed water-meadow community, Salisbury (1965) reckoned that the average plant produced less than 200 seeds and, locally, the figure could be appreciably lower than this estimate.

Seed dispersal

Seeds are shed explosively, by the sudden splitting and coiling of the valves of the ripe fruit, a mechanism which can fling the seed up to a metre or more. The seed coat is mucilaginous and becomes sticky when wet, a feature which undoubtedly enables secondary distant dispersal by attachment to the feet of animals and perhaps also to bird feathers (Salisbury 1965).

Seed longevity

Buried seed survival is a matter of some dispute, there being many measurements and estimates suggesting it is transient, or short-lived and a few indicating longer term seed persistence and viability for up to five years or more (Thompson et al. 1997).

Vegetative reproduction

It has been known since 1825 that C. pratensis can reproduce vegetatively by the production of tiny adventitious viviparous plantlets on the leaves (Smith 1825, 3, p. 190). Salisbury found that these plantlets developed from cells over the veins on the upper surface of the terminal leaflet of radical leaves and to a lesser extent from other leaflets on the basal leaves. He also confirmed rooting from axillary buds took place (Salisbury 1965, p. 331). C. pratensis can carry out additional forms of vegetative reproduction, by branching of the short rhizome, or from plant fragments (ie broken stems and leaves), all of which are capable of rooting. So frequent and successful are these asexual processes in multiplying and dispersing the plant − particularly in the wetter habitats of the species − that Salisbury reckoned vegetative reproduction was probably the predominant mode of increase of C. pratensis in moist ground. The resultant clonal development could help explain the species' low seed production, since it would be possible for all the plants in flower at one time to belong to the same clone and thus self-incompatibility would block seed set.

The frequency of the vivipary is known to vary markedly with habitat conditions and Salisbury acknowledges that it is commoner in "the wetter situations". He quotes White's (1912) Flora of Bristol, where the latter comments that, "the plant multiplies freely by a process of proliferation from leaflets of the lower prostrate leaves", and, "repeated examinations of plants in the field have shown that over 70% are viviparous − more in bogs, less in dry places".

Plants have been examined in mown and unmown roadside wet grassland in Fermanagh, Down (H38) and West Cork (H3), none of which showed any evidence of vivipary whatsoever. It would be an interesting project to examine throughout B & I the frequency of vivipary in this and in other species in which it is reputed to occur. Salisbury (1965, p. 335) lists vivipary as occasional in Drosera rotundifolia (Round-leaved Sundew) and more rarely occurring in D. intermedia (Oblong-leaved Sundew). Buds have been recorded as arising from leaves of various other Brassicaceae (Cruciferae) − see the species account of C. flexuosa for more details.

Hybrids

An extremely similar reproductive strategy, also heavily dependent upon specialized foliar and axial vivipary, is described for the triploid hybrid C. × insueta (C. amara L. × C. rivularis Schur), from hay meadows and open pastures in Central Switzerland by Urbanska (1981). This and other studies emphasises that we should always remember that reproductive capacity may be largely influenced by environmental conditions.

A hybrid between C. pratensis and C. amara (C. × ambigua Schulz (C. × mixta Druce)) has been reported from Oxfordshire (VC 23), but Stace (1975) commented that the little hybrid seed produced from many pollinations between these species proved inviable and thus reputed wild hybrids reported both in the BI and on the Continent, require verification.

British and Irish occurrence

Reflecting its powers of seed dispersal, C. pratensis is found throughout the whole latitudinal range of Britain, from the Channel Isles to the tip of Unst in the Shetland Isles. However, it is not omnipresent, being absent from some of the smaller western isles of both Britain and Ireland and also from sections of the SW coast of Ireland and from parts of the English Wash (Preston et al. 2002).

European and world occurrence

Due to the unclear pattern of variation and confused taxonomic position of the C. pratensis species group or aggregate in B & I, in their European treatment of its distribution, Jalas & Suominen (1994, Map 2350) mapped the seven subspecies of the C. pratensis group together as one species. They also mapped the component taxa separately − most of which are either absent or poorly represented in B & I.

The European distribution of the C. pratensis group shows it as native and widespread throughout the Continent, but becoming scarce towards the S & SE and absent from most of Greece and all of the Mediterranean islands. Hultén (1971, Map 72) shows the C. pratensis group continuously distributed around the northern hemisphere and also present as an introduction in New Zealand.

Trends

Populations of C. pratensis probably have declined or been destroyed in B & I during the last 50 years, due to agricultural drainage and the increased use of agrochemicals, although there is some suggestion that the species may contain genotypes resistant to some herbicides (Rich 1991). The New Atlas (D.A. Pearman, in: Preston et al. 2002) suggests that there has been no overall change since the earlier BSBI Atlas (Perring & Walters 1976) but this is the picture when working at 'the one record in a 10 km square' level of discrimination.

Casual and garden forms

Cuckooflower does occasionally occur as a casual garden weed of damp, heavy soils and most especially of lawns. The latter is not really surprising, since recent mowing experiments in an abandoned fen meadow showed this treatment had a positive influence on population survival of C. pratensis and other typical wet meadow species (Jensen & Meyer 2001).

Double flowers are also sporadically found in the wild and in Fermanagh, as elsewhere, these are often brought into garden cultivation. Small populations of 'normal' C. pratensis have been reported from neglected damp grassy areas in suburban gardens in Dublin city and these plants are considered a consequence of the increasing commercial trade in 'wild flower seed mixtures' (Scannell 1997).

Folklore and names

The fact that this species has so many English common names (Grigson (1987) lists no less than 53) suggests that it must have numerous traditions associated with it. Many of the local names have springtime associations, eg involving the cuckoo which sings in April and May, or names which contain 'May' as an element, or lambs. Other names involve milkmaids and their smocks, or the lady (ie our lady, the Virgin Mary), pigs, pigeons and their eyes. Grigson (1987) gives quite a detailed account of these names, their sexually suggestive connotations and the tradition of ill luck if they are picked (an alternative name is 'Pick-folly'). Vickery (1995) also recounts several witnesses to the ill luck on flower gatherers. Several folk names include mention of 'blobs' and these and the references to 'milk' may readily be connected with the familiar sight of 'cuckoo-spit' on the plant − the white foam protecting frog-hopper nymphs from predators. In his Dictionary of English Plant Names, Grigson (1974) enlarges on the origins of the two most frequently met names, 'Cuckoo-flower' and 'Lady's Smock' in similar vein. Another general name for the genus is 'Bittercress' and the young leaves do have a peppery taste and have been used as a Cress substitute in salads and sandwiches (Mabey 1996, p. 151).

There are two notions regarding the origin of the genus name 'Cardamine'. It is either derived from two Greek words 'kardia' meaning 'heart', and 'damao' meaning 'subdue', a reference to its medicinal properties as a heart sedative (Johnson & Smith 1946; Chicheley Plowden 1972), or it may simply be a carry over of an ancient Greek name given to some cress-like herb in the Dioscorides herbal (Gilbert-Carter 1964; Stearn 1992). The Latin specific epithet 'pratensis' simply means 'growing in meadows' (Gilbert-Carter 1964).

Threats

None.

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