Barbarea vulgaris W.T. Aiton, Winter-cress

Account Summary

Growth form and preferred habitats

B. vulgaris is a widespread, sometimes abundant biennial (infrequently a winter annual), or a short-lived perennial weed that avoids competition by frequenting disturbed habitats. The very dark, shining basal rosette leaves, shallowly lobed stem leaves and deep to bright yellow flowers with a slender style make Winter-cress a distinctive wintergreen rosette-forming crucifer, readily enough distinguished from B. intermedia (Medium-flowered Winter-cress), which is the only other member of the genus widely found in N Ireland (Rich 1987a; An Irish Flora 1996; New Atlas).

Typically, it grows in disturbed ruderal sites such as roadsides, waste ground, farmyards, around quarries and on damp, winter-wet soils in field margins, ditches and beside woodland paths, or other shaded or semi-shaded waysides or waterside habitats. The plant develops a stout taproot which often exceeds 50 cm in depth, and it also produces an extensive branched fibrous secondary root system that allows it to readily cope with dry soil environments.

Winter-cress has no specific substrate requirements and will grow on a very wide range of soil textures and levels of fertility. It is absent mainly from the more extreme acidic soils and also from both vigorous closed-turf grassland (where it cannot compete effectively) and full-canopy woodland (where autumn leaf litter cover encourages slugs which devour its young seedlings). Essentially it is an opportunistic coloniser of open habitats and individuals of B. vulgaris grow most rapidly, live longest and reproduce most prolifically on recently disturbed, moist, fertile soil (MacDonald & Cavers 1991).

As with poppies (Papaver spp.), a widespread persistent seed bank exists allowing B. vulgaris to often appear in a recurrent manner, sometimes in great abundance on freshly disturbed ground, eg along road widening schemes and by recently cleaned or canalised waterways.

Weedy properties

The weediness of B. vulgaris is based on a combination of three factors: (a) the ability to increase numbers rapidly through high rates of seed production (ie there is an estimated seed production of between 40,000-116,000 seeds per plant in a hayfield situation, or 88,000 per plant in a tilled, weeded site (Kott 1963 (in Russian), quoted in MacDonald & Cavers 1991); (b) inedibility of the rachis of the flowering stem at maturity, due to the presence of toxins; and (c) long-term seed dormancy - surviving over five years burial in soil (Roberts 1986), and according to MacDonald (1977), it can survive for at least 10-20 years, thus permitting intermittent recruitment to the population when conditions are favourable for germination and establishment.

Temperature as a limiting factor

The geographical range of Winter-cress is limited to areas where its obligatory requirement for seed vernalisation is met. This requires exposure to temperatures of 5°C or less for several weeks to break seed dormancy, which itself is imposed in the autumn after seed production by either drought and/or cool temperatures, ie below 10°C. This cool temperature requirement for successful overwintering seed survival sets a limit to the southern spread of the species, so that recurrent populations are best maintained in areas with periods of low rainfall in late summer and cool temperatures from late summer to early spring.

Rosettes of B. vulgaris will grow at or below temperatures of 5°C, but bolting of the flowering stem only takes place after ambient temperatures rise above 10°C for more than one week (MacDonald & Cavers 1974). The northern limit to its range is about 60°N (Jalas & Suominen 1994), and this is probably related to the length of the reproductive season permitting seed-set after this temperature has been reached (MacDonald & Cavers 1991). The New Atlas hectad map makes it quite obvious that Co Fermanagh is close to the climatic NW limit of the species' overall European range.

Fermanagh occurrence

In Fermanagh, B. vulgaris is a widespread and locally abundant weed species. It has been recorded in 134 lowland tetrads, 25.4% of those in the VC.

Fossil record and status

B. vulgaris is regarded as native in both B & I, fossils from previous interglacial periods (the Hoxnian and the Ipswichian), lending weight to the case for the current interglacial, although the only record listed by Godwin (1975) came in fact from a Roman settlement, and could therefore easily be argued to indicate an ancient introduced species (ie an archaeophyte).

British and Irish occurrence

B. vulgaris is the commonest of the four species of the genus found in B & I, with only the introduced B. intermedia (Medium-flowered Winter-cress) rivalling it in distribution and abundance, and even then it does so only patchily and apparently very much more frequently in N Ireland than in the RoI (New Atlas). Although certainly widespread in the both B & I, B. vulgaris becomes rarer or absent in westerly regions of both islands throughout the whole latitudinal range. In Scotland, it becomes more coastal the further north one goes and eventually it peters out towards the NW, at least as a presumed native species (Preston et al. 2002).

European and world occurrence

Beyond B & I, the species, which is probably of Mediterranean origin, is considered native across most of Europe south of latitude 60°N, extending east to the Himalaya. B. vulgaris is absent from the Balearic Isles, rare in Sardinia and absent also from Crete. It is a widespread introduction throughout Scandinavia and to a much lesser extent in Iceland (Jalas & Suominen 1994, Map 2304). Elsewhere, it is an introduction in N Africa, N America (where it is classified as a noxious weed) and Australasia (Rich 1991).

Growth and flowering reproduction

In B & I, most germination and vegetative growth of B. vulgaris occurs early in the spring, but seedlings emerge throughout the year from seeds brought to the surface by disturbance. In milder, sheltered areas of these islands, growth of the rosette is almost continuous (Baskin & Baskin 1989). When germination occurs in favourable autumn conditions, the plants produced will be either winter annuals or perennials, while spring germinating plants tend to be biennial or perennial. Very shortly after spring temperatures reach 10°C, the rosette, provided it is large enough and has accumulated sufficient stored photosynthetic resources, will bolt and produce the flowering stem.

The flowers are primarily out-crossed, possess nectar and attract Hymenoptera (bees and butterflies) plus beetles and flies. Probing by these insects for flower foods causes both self- and cross-pollination. In dull, cool weather when insect visitors are rare, the two shorter stamens of the six in each flower, bend towards the stigma and effect self-fertilisation (Proctor & Yeo 1973; MacDonald & Cavers 1991).

Seed production and dispersal

The seeds are small and light and the number per fruit (ie siliqua) ranges from 3 to 21 with a mean of 13 (Salisbury 1942). As previously mentioned, given suitable ecological conditions, the overall seed output per unit area can be enormous, but the plant has no specialized dispersal mechanism and the majority of seeds are simply dropped from the septum within a metre of the parent plant. The actual primary dispersal distance of seed depends on plant height, surrounding vegetation, temperature, humidity and wind speed (MacDonald & Cavers 1991). There may be, however, some very occasional secondary dispersal, since the seed coat is covered with an adhesive mucilage that, when moistened, may either inhibit dispersal by sticking the seed to soil particles, or promote transport by attachment to the surfaces of passing animals.

Ridley (1930) quotes records of B. vulgaris growing as an epiphyte along with 75 other species in the soil accumulated on the tops of pollarded willows in Cambridgeshire (VC 29), which one presumed must have been blown on high, or have been carried aloft by birds. Winter-cress seeds are said to be bitter tasting, yet they have been recorded in the droppings of numerous animals including horses, cattle, pigs and rabbits. The seed remains viable after passage through the gut of these animals, providing secondary dispersal by internal zoochory (ie endozoochory) (Salisbury 1964). They can also survive continuous immersion in water (and presumably also in flooded soil) for up to eight weeks (MacDonald & Cavers 1991).

Vegetative reproduction

Occasionally, and particularly after physical damage to the inflorescence, B. vulgaris produces what have become known as 'cauline rosettes' on the bolted stem of the inflorescence late in the season after flowering has been completed. This can lead under certain circumstances to asexual reproduction and dispersal (MacDonald & Cavers 1974; Rich 1984). Cauline rosettes are similar to small basal rosettes but are produced in the axils of stem leaves and, if they come into contact with the ground, they can form adventitious roots and may become independent, thus establishing new clonal plants. If these rosettes succeed in overwintering, they will flower the following year. The fact that prior damage to the plant appears to be involved probably indicates that cauline rosette formation is triggered by a physiological or hormonal imbalance, but it is rather surprising that these asexual organs have only been reported in this one crucifer species (Rich 1984).

Variation

B. vulgaris is a very variable species, and in terms of both size and robustness it reflects habitat conditions so strongly that Jackson (1916) recognised four varieties within it. Rich (1987a) discussed these forms fully, but reckoned that the subdivisions require more study over the whole geographical range of the species and, until this is completed, he felt it better regarded as a single highly polymorphic species. Rich (1991) mentions that the species is even more variable in the rest of Europe than in Britain, a not unexpected fact considering the greater range of environmental conditions available there. However, in the absence of a more convincing native fossil record, this lends further credence to the possibility that in common with the three other Barbarea species found in B & I, B. vulgaris might well be an ancient introduction. Double-flowered and variegated garden forms of B. vulgaris have also been described.

Names and uses

The genus name 'Barbarea' is derived from the fact that the plant was once dedicated to Saint Barbara (Herba Sanctae Barbarae), the patron saint of artillerymen and miners, and protectress in thunderstorms (Gilbert-Carter 1964; Stearn 1992). The reason for the dedication is probably because the plant is wintergreen and has generally grown to a substantial size around the Saint's feast day (Dec. 4 - old style), when people collected rosettes to eat as a source of fresh green vegetable, a custom that dates back to the 14th century. A 100 g serving of the fresh green leaf provides 130 mg of vitamin C (more than twice the 60 mg recommended daily human requirement) (Zennie & Ogzewalla 1977; MacDonald & Cavers 1991). The plants do however produce a number of mustard oils, including sinigrin which gives it a rather tangy taste, and too large an intake would prove toxic, although there are no reports of this actually happening in B & I (Cooper & Johnson 1998). The Latin specific epithet 'vulgaris' meaning common, is quite appropriate in this instance.

Several of the English Common names include 'Cress', a general name applied to many members of the Cabbage family, and known from all the Germanic languages from the earliest times, also adopted into the Romanic and other dialects, but of quite unknown origin (Prior 1879). The names include 'Wintercress', of obvious relevance, 'Land Cress', as opposed to 'Watercress', 'French Cress' 'Yellow Cress' and 'St. Barbara's Cress'.

Several other names include 'Rocket' (e.g., 'Yellow Rocket', 'Winter Rocket' and 'Wound Rocket' ), which is derived from a supposed similarity to the hot-tasting plant Eruca sativa, Rocket, which was called in Italien 'ruca', diminutive 'ruchetta', and in French 'roquette', and thus very readily became 'Rocket' in English (Grigson 1974). The name 'Wound Rocket' was given by Turner in the Names of Herbes (1548), since he felt it had leaves like Rocket and was good for a wound remedy, but the name was never adopted and the current author can find no reference giving the plant any medicinal use (Grigson 1987). One of the most unusual names from southern England is 'Cassabully', for which the current author can offer no explanation, except that 'caisse' is French for a purse or money-box, like the Latin 'capsa' (Britten & Holland 1886).

Threats

None.

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