Cardamine flexuosa With., Wavy Bitter-cress
Account Summary
Native, common, widespread and locally abundant. European temperate, but also in C and E Asia and possibly introduced in eastern N America.
1881; Stewart, S.A.; Co Fermanagh.
January to November.
Growth form, species origin and preferred habitats
Morphologically very similar and genetically very closely related to C. hirsuta (Hairy Bitter-cress), most Fermanagh records have been distinguished from the latter on the 'jiz' of the plant (ie overall size, leafiness and hairiness of the stem), plus the number of stamens, ie plants having a preponderance of six anthers were taken to be C. flexuosa. While C. hirsuta is always an annual species, C. flexuosa is very much more variable in terms of life-form and it can be either annual, biennial (ie a short-lived monocarpic perennial), or even a polycarpic (repeat flowering) overwintering perennial (Grime et al. 1988; Webb et al. 1996). When it is behaving as an annual, C. flexuosa can germinate in the autumn − germination probably under day-length control and, in this case, it overwinters as a small wintergreen leaf rosette. Alternatively, the seed may undergo chilling and vernalisation, so that germination is delayed until the springtime.
The flexibility in life-form which C. flexuosa can assume, allows it to exploit a variety of ecological situations, ranging from the colonisation of temporarily open, bare ground or unoccupied litter, to persistence in a rather more closed vegetation cover − where the species can persist as a biennial or as a perennial, always provided conditions such as grazing, seasonal shade or flooding, ensure that competition is not excessive, or sufficient to oust the plant.
Wavy Bitter-cress is a tetraploid (2n=32), which is believed to have arisen by allopolyploidy from a sterile hybrid between C. hirsuta and C. impatiens (Narrow-leaved Bitter-cress) (both 2n=16), followed at some stage by chromosome doubling to create the new, fully fertile species (Ellis & Jones 1969).
Since C. flexuosa and C. hirsuta are so closely related, they share many of their ecological requirements and tolerances. Thus they overlap in their many habitats and may occur together, making their distinction even more uncertain at times. However, having hybrid origin, C. flexuosa tends to be the larger and more lax in growth of the two species, but it is not necessarily the more vigorous, or the more floriferous plant.
Comparative competitive ability
Neither of these two Cardamine species has much competitive ability, so they tend to occupy either bare soil or mud, or gaps in vegetation cover produced by some form of moderate disturbance that minimises negative interaction with more aggressive, robust herbaceous species. Very early, rapid seasonal growth and the ability to self-fertilise their tiny flowers characterises both these Cardamine species, allowing them to successfully reproduce earlier than most associated species present in the wide range of habitats they frequent.
C. flexuosa prefers, or is more restricted to, somewhat damper, deeper, moderately fertile and acidic, organic soils (but not in strongly acidic or permanently wet conditions), in comparison with C. hirsuta. Of the two species, it most typically frequents cooler, more sheltered, semi-shaded situations, where the likelihood of desiccation is reduced or minimised, although in these habitats it sometimes has to compete with its close relative.
In the Sheffield area of England, C. flexuosa was categorised as intermediate between a stress-tolerant ruderal and a ruderal species by Grime et al. (1988). In the current author's (RSF) view, however, this classification would exaggerate the level and frequency of disturbance that C. flexuosa faces in its typical Fermanagh habitats which are more semi-natural than urban in character.
Fermanagh occurrence
C. flexuosa is much more frequently found than C. hirsuta in woods and by stream-sides, lakeshores and in shaded, sheltered, damp rural places in general – including waysides, cliffs and overgrown areas in old quarries. Since these are common situations in Fermanagh, it is not surprising that C. flexuosa has been recorded more than 2.5 times as frequently as C. hirsuta in the county and in very nearly twice as many tetrads, ie in 291 tetrads, representing 55.1% of those in the VC.
Flowering reproduction
Quantitative data on the flowering and seed production capacity of C. flexuosa seem unavailable, but both are probably very similar to those of C. hirsuta. As in other Cardamine species, seeds are explosively released and may be flung up to a metre from the parent plant. The soil seed bank of C. flexuosa is less persistent than that of C. hirsuta, the seed being classified as either transient, or surviving at most one year in the ground (Thompson et al. 1997).
Vegetative reproduction
C. flexuosa is capable of vegetative reproduction by the rooting of shoot fragments broken off and transported as a result of disturbance (Grime et al. 1988), but so far the extent or significance of this appears to be unstudied. Salisbury (1965), writing of the viviparous plantlets produced on leaflets of C. pratensis, mentions that buds have been recorded arising from leaves of various other members of the Brassicaceae (Cruciferae), and he lists six species, including C. flexuosa, C. hirsuta and C. impatiens (Narrow-leaved Bitter-cress). He points out, however, that, "... there is a suspicion that some at least of these may have been axillary buds that had developed roots ... " (ie rather than leaf cells giving rise to plantlets), "... so they are not comparable", ie with the viviparous situation he was describing in C. flexuosa (Salisbury 1965, p. 335).
British and Irish occurrence
While common and widespread throughout most of B & I, the New Atlas shows C. flexuosa is less well represented in the Irish midlands and on the extreme W coast, while in Scotland it thins out towards the NW, and in E England it is absent from parts of Cambridgeshire, S Lincolnshire and SE Yorkshire (Preston et al. 2002). At the same time the distribution is not considered to have changed since the earlier BSBI Atlas (Perring & Walters 1976).
European and world occurrence
In continental Europe, C. flexuosa has a markedly western distribution (not extending much further east than Poland) and thinning towards the south and absent in many of the Mediterranean islands. To the north, it is more extensively represented in Scandinavia than C. hirsuta but, unlike it, C. flexuosa is absent from Iceland (Rich 1991; Jalas & Suominen 1994, Map 2375). Although the taxonomy is uncertain, five related forms (possibly subspecies) are believed to occur in the Himalaya, E Asia and the Philippines (Hultén 1958, Map 125; Grime et al. 1988; Rich 1991). Thus C. flexuosa is polymorphic, and the subspecies (or perhaps related species) are widely disjunct in their distribution around the N Hemisphere (Hultén & Fries 1986, Map 934). Subsp. flexuosa is also sparsely present in eastern N America. It is claimed by some to be native there, and therefore amphi-Atlantic, but it is much more likely an introduction, as is definitely the case in Australasia.
Names
The Latin specific epithet, 'flexuosa' is derived from 'flecto' meaning 'bend' or 'curve' and refers to the rather wavy, flexuous flowering branch typical of the species (Gilbert-Carter 1964).
C. flexuosa is not sufficiently distinguished from C. hirsuta to have any English common names associated with it.
Threats
Very possibly capable of further increase in fertile, disturbed ground, but probably not endangering any other native species in doing so.