Nasturtium officinale s.l. (= Rorippa nasturtium-aquaticum agg.), Water-cress

Account Summary

Taxonomy and recent changes

Formerly all white-flowered water-cresses were regarded as belonging to a single species, Nasturtium officinale R. Br. s.l., and Druce (1932), in his Comital Flora of the British Isles, recorded it as occurring in every VC in B & I. This entity was subsequently split in the mid-1940s into two species and their intermediate sterile hybrid (Howard & Manton 1946). The three forms subsequently changed genus from Nasturtium to Rorippa, section Cardaminum, so that for a time we recognised them as R. nasturtium-aquaticum, R. microphyllum (Narrow-fruited Water-cress) and R. × sterilis (Hybrid Water-cress) (Rich 1991; Stace 1997). Recent analysis of chloroplast DNA and nuclear encoded ITS sequences has confirmed, however, the separation of Nasturtium from Rorippa Scop. (Franzke et al. 1998; Bleeker et al. 1999), so we have seen a return to Nasturtium nomenclature for these three taxa (Stace 2010, 2019; Sell & Murrell 2014).

In terms of their vegetative form, specimens of the two white-flowered water-cress species and their hybrid are very variable with respect to their growing conditions, ie they are phenotypically very plastic with respect to their environment (Rich 1991). This means that when we are making observations in the field we are forced to accept that we cannot distinguish non-flowering, vegetative water-cress material of N. microphyllum from either N. officinale, or their hybrid, and we are obliged therefore to record such indeterminate plants simply as N. officinale s.l.

Following what has now become the preferred botanical practice, we will continue to keep records of the species aggregate separate from N. officinale (= R. nasturtium-aquaticum s.s.).

Fermanagh occurrence

The situation in Fermanagh is that what we now call N. officinale s.l. has been commonly recorded in a total of 249 tetrads, 47.8% of those in the VC. It is very widespread throughout, being present in all forms of marshy ground, including wet meadows, by lakes, streams, springs and ditches.

A very interesting Biological Flora account of Nasturtium officinale R. Br., by Howard & Lyon (1952a), describes the ecology and biological behaviour of the plant in detail, but since the information given really applies to the species in the strict sense, it will be dealt with by us under that species account.

European and world occurrence

N. officinale s.l. is also common and widespread throughout W & S warm temperate Europe, N Africa and eastwards to C Asia, but due to the change in taxonomy of the species aggregate, plus the fact that water-cress has been cultivated for at least 2,000 years, it is not really possible to delimit its native occurrence (Hultén 1971, Map 195). The plant in this broad taxonomic sense has also been introduced to N & S America, S Africa, the Far East and to Australasia (Rich 1991).

Uses

Watercress has been eaten either raw as a rather spicy, peppery salad, or boiled as a green vegetable, by people of all ranks for many centuries. Following another of the periodic slumps in agricultural fortunes, it has been commercially farmed in the midlands and the south of England since about 1808, and found a niche in suitable places with a supply of clean, flowing, lime-rich water (Grigson 1987; Thrisk 1997, pp. 204 & 295 ). The fact that cultivation has really only been successful along those streams that draw their water from deep in the English chalk may be due in part to the limey composition, purity and alkalinity, but it is also true that in winter these deep-welling waters tend to be warmer than their surroundings, giving the aquatic plant a more favourable growing environment than streams fed by local rainfall or snow melt (Edlin 1951).

Watercress farmers used to grow both N. officinale, 'Green Cress' and N. x sterilis 'Brown Cress' for salad, and actually prefer the latter, but much earlier than its cultivation as a salad crop Watercress had a deserved reputation among herbalists for the prevention of scurvy, few plants being richer in vitamin C. Watercress was traditionally picked wild from the edges of streams and ditches, where it can grow in thick drifts. It is, or rather used to be, sufficiently important and valued a plant for numerous English settlements to be called after it, e.g., names beginning with 'Kes', such as 'Kersey' in Suffolk, derived from 'Cress island', and 'Kershope' in Cumbria, derived from 'Cress valley' (Mabey 1996).

Perhaps one of the reasons for the longstanding popularity of watercress salad in B & I is suggested by Glenny (1897), who noted that compared with Continental Europe and the Far East, where (at least until fairly recently), people traditionally ate far more salad herbs than we do, and they dress the bowl with "Lucca oil, vinegar, mustard and salt, or most of these, properly incorporated with the raw herbs", whereas in these islands, Watercress is "at least amongst the lower and middle classes, preferably eaten in a simple and primitive way", ie alone, unadorned, and often not even mixed with other greens as, "it loses its individuality when partaken with any other herb" (Glenny 1897, p. 608). Mabey (1972, p. 75-77) and (1996, p. 147-148) recounts interesting first hand descriptions of the Watercress trade in Victorian London. He also gives sensible warning advice on the choice of plant material to avoid the dangers of liver-fluke, which due to the presence of a snail as a secondary host of the parasite on the leaves, often infests Watercress plants anywhere near sheep or cattle pastures.

In more recent times Watercress has several times gone in and out of fashion, its culinary use sometimes reduced to just a few sprigs garnishing steak, until it is promoted by a celebrity chef and suddenly its use revives. Until the mid-1950's hybrid 'Brown-' or 'Winter-watercress', R. x sterilis was the preferred plant on acount of its somewhat greater frost-resistance and year-round leaf production, but continual reliance on vegetative propagation led to susceptibility to disease, and a mosaic virus and two fungal pathogens causing 'Crook root' and 'Cabbage black ring spot' quickly led to its abandonment. Farmers turned instead to N. officinale, 'Green watercress', which is fertile and whose propagation from seed avoids virus infection. Selective breeding of N. officinale sens. str. since then has been directed towards disease resistance, prolonging the vegetative stage by delayed flowering, and developing a growth form which facilitates mechanical harvesting (Bleasdale 1964; Crisp 1976).

At the same time there has been a reduction in the area of commercial growing in England, with British-based companies developing watercress cultivation abroad in both continental Europe and in N America in order to maintain supplies in wintertime. There is also evidence on the World Wide Web that commercial Watercress cultivation, sometimes involving hydroponic, is currently being explored and encouraged by government agencies in New Zealand, and there are now at least 24 franchised growers there spread over both islands. In North America too, Watercress cultivation is carried on in five eastern states on a large scale.

Names

The English name 'Cress' generally refers to this plant, ie 'Watercress', or 'Garden Cress' (Lepidium sativum). The name derives from the Old English (OE) or Anglo-Saxon 'caerse', 'cerse', or 'cresse', with similar cognate names in other Germanic languages, all based on an Indo-european word meaning to nibble or to eat. In OE, N. officinale sens lat. or the species aggregate was distinguished as 'ea-cerse', meaning 'stream-cress', or 'wielle-cerse', 'spring-' or 'brook cress' (Grigson 1974).

Grigson's famous 'Englishman's Flora' lists eleven English Common names chiefly based on the OE name, although he also includes the Yorkshire 'Tang-tongues', which Britten & Holland give as 'Teng-tongues', referring to 'Water-cresses as being pungent to the taste' (Grigson 1987; Britten & Holland 1886). Another English Common name Grigson lists, which originated in Gloucestershire, is 'Carpenter's Chips', a clear reference to the chip baskets (ie baskets of unbarked (or stripped) willow), in which the Watercress crop was often shipped to market (Edlin 1951, p. 59).

Threats

None.

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