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Lepidium heterophyllum Benth., Smith's Pepperwort

Account Summary

Possibly introduced, very rare. Apparently oceanic southern-temperate, but the native range is uncertain.

1950; MCM & D; abundantly by the roadside south of Glenross.

Growth form and preferred habitats

L. heterophyllum is a rather weedy rosette-forming perennial, or more rarely a biennial plant with a stout woody rootstock and branching grey-green stems 10-50 cm tall. The basal leaves disappear before flowering, but they subsequently re-sprout after fruiting (Clapham et al. 1962). The numerous prostrate or more or less procumbent flowering branches are clothed throughout the season with many crowded, short, stem leaves, both toothed at the side and with auricles at the base to varying degrees.

The species colonises dry, disturbed lowland ground, as well as arable fields and dry, open pastures. It appears to avoid calcareous conditions (being something of a calcifuge) and often is a plant of dry acidic soils on heaths and gravelly places by paths, roadsides verges, alongside railways and on well-drained embankments. In other parts of the B & I, it is frequent on seashore shingle and, to a much lesser extent, it also appears in arable fields and short-turf pastures, where we can assume competition is of a low order. The established strategy of L. heterophyllum is categorised as SR/CSR, ie intermediate between a stress tolerant ruderal and a competitor-stress tolerator-ruderal (Grime et al. 1988 & 2007).

Flowering reproduction

Terminal clusters of numerous small, white flowers are produced from May to August or September and the violet or reddish anther colour (prior to their bursting) is a useful distinguishing character from L. campestre (Field Pepperwort) which is otherwise similar, but which has yellow anthers (Rich 1991; Webb et al. 1996). American common names for the plant are 'Purple Antherfield Pepperweed' and 'Variable leaved Pepperweed', both of which are helpful reminders of significant identification features of the species. The flowers appear to be self-fertilized and the fruits contain just one 2 mm diameter seed in each of their two compartments (Fitter 1987).

In ecological terms L. heterophyllum appears to be a fairly undemanding plant of dry, sunny, infertile, open, more or less disturbed, stony conditions where competition is fairly minimal or repressed (Sinker et al. 1985). L. heterophyllum is also said to be tolerant of grazing pressure (Rich 1991) − probably because, like L. latifolium (Dittander), its roots and leaves taste burning and bitter (Gerard 1597; Grigson 1987).

Just as there appears to be little or almost nothing written on the ecology or biology of this species, there is likewise no mention of its dispersal mechanism, seed longevity or germination in any of the literature the current author (RSF) has consulted (eg Ridley 1930; Grime et al. 1981; Thompson et al. 1997). Clearly, if we are ever to understand what governs the occurrence of widespread plant species like this one, we must have some more basic biological research data to fill such obvious gaping holes in our knowledge. However, the ecological behaviour of L. heterophyllum and L. campestre (Field Pepperwort) appears rather similar and their British distributions appear so complementary (L. heterophyllum declining in the SE, which is the principal area of L. campestre), that one might suggests that the latter could possibly be competitively excluding the former (Preston et al. 2002).

Fermanagh occurrence

Although very rare in Fermanagh, L. heterophyllum is by far the most common Lepidium species in NI. It is generally reckoned to be a native species in Ireland, as is also the case in Britain. However, there are only four Fermanagh records, three of which date from 1950. It has been found by RHN in only one site recently. Apart from the first record given above, the remaining details are: sand pit near Killadeas, 1950, R. Mackechnie; roadside 1.5 km W of Tempo, 1950, MCM & D; old Quarry at Lisbellaw, 3 July 1994, RHN.

Questionable native status of the species

While in Fermanagh this species is very rare and occupies, or once did, disturbed ground on roadsides, quarries and sand-pits, RHN thinks it might possibly be an introduction, or an escape from arable cultivation. Elsewhere, in quite a wide portion of B & I, L. heterophyllum is a fairly frequent or local, uncompetitive species of dry, acid, sandy, gravelly or heathy soils. It is also a frequent species of coastal shingle, railway ballast and embankments and less commonly appears in arable ground and in dry, open pastures. The current author (RSF) finds it difficult to accept that the status of this grey-green crucifer species is different in Fermanagh from everywhere else in the British Isles. However, we might well ask, what real evidence is there for regarding this species as indigenous in these islands? There does not appear to be any fossil record of the species (Godwin 1975), so we are left to consider circumstantial evidence to determine its status (Webb 1985).

Rich (1991) suggests that L. heterophyllum is native in Europe from Spain to Czechoslovakia and is "occasionally introduced elsewhere in Europe". Jalas et al. (1996), in Atlas Florae Europaeae, 11, map the species as being native only in W Europe (Spain, Portugal, France and the British Isles), but they believe the species is probably or more definitely introduced in regions from the Netherlands northwards into Scandinavia, and entirely absent from Italy and more easterly and more continental European regions (Jalas et al. 1996, Map 2787). It is introduced in N America and Australasia (Rich 1991).

There is no space here to further argue the case, but the current author (RSF) concludes that in common with other widespread weeds of disturbed ground, the native distribution of L. heterophyllum is basically unknown and remains a disputable subject. The status of all such species in botanical literature owes more to tradition than to science. Currently developing genetic techniques should, however, eventually allow an analysis of species cytotypes and this may then provide definitive answers to questions of native occurrence of weedy species such as this one.

British and Irish occurrence

In view of its weediness, it is rather surprising that L. heterophyllum is not more generally distributed in B & I than it is. The New Atlas shows it most commonly distributed along the Irish Sea coasts of both islands, plus the S coast of Ireland and NE Scotland, but only scattered and much rarer elsewhere across these isles. It is either entirely absent or very rare in the Midlands and the west of Ireland (Preston et al. 2002).

Names

The genus name 'Lepidium' is a Greek name used for some plant by the classical botanist Dioscorides and is the diminutive of the Greek word 'leptis' meaning 'a scale', the fruits of Lepidium being considered scale-like (Gilbert-Carter 1964; Stearn 1992). The Latin specific epithet 'heterophyllum' means 'other leaves', or 'diverse leaves', that is the plant has leaves of different forms (Stearn 1992).

Previously, the botanical name of the plant was L. smithii, called thus in honour of Sir James Edward Smith (1759-1828), author of the influential English Botany and much else (McClintock 1966, pp. 82-4). This connection is retained in its current recommended English common name, 'Smith's Pepperwort', sometimes also given as 'Smith's Cress' (Melderis & Bangerter 1955). Other more descriptive common names include 'Downy Pepperwort' and 'Hairy Pepperwort', the former the more accurate since the whole plant is usually (but not always) well furnished with a soft pubescence of short, grey, simple (unbranched) hairs. The American name 'Purple Antherfield Pepperwort', provides a reminder of the simple differential character between this species and L. campestre, with which it probably is most often confused.

The name 'Pepperwort' was first used by Turner (1568) for L. latifolium (Dittander), which in the 16th century was cultivated for its roots and leaves that were used in making hot pungent sauces until pepper and Horse-radish drove it out (Grigson 1987). Gerard (1597, 1633, p. 240) says "the root is sharp and biteth the tongue like pepper, whereof it tooke the name pepperwort".

Threats

None.