Lysimachia nemorum L., Yellow Pimpernel

Account Summary

Growth form and preferred habitats

The reddish stem and ovate, acute, entire, opposite leaves make this creeping and trailing, yellow-flowered perennial unmistakable. While the slender, ± prostrate stems and thin herbaceous leaves might appear delicate, the plant is completely frost hardy and evergreen, but it is not regarded as long-lived. L. nemorum is frequent and sometimes sufficiently abundant to form dense mats or loose carpets in damp, lightly shaded ground. Typical habitats are damp to dry, poorly-drained, winter-wet or flushed, nearly bare soil patches found in woods, scrub, on lakeshores, or by tracks, hedge- or river-banks, shady ditches, or in more or less marshy grassland. It also occurs in shady spots in upland glens and on cliffs. L. nemorum prefers quite fertile or base-rich soils of medium reaction (ie moderately acid to neutral pH levels).

Yellow Pimpernel is absent, however, anywhere vegetation becomes densely shaded, or where the turf becomes rank, tall or over dense, or where leaf and branchlet litter accumulates. Bare or only vernally occupied, open disturbed ground is essential for colonisation and establishment, allowing L. nemorum to avoid competition from more vigorous, taller, or larger-leaved species (Sinker et al. 1985; A.J. Richards, in: Preston et al. 2002). The necessary environmental conditions for limited growth potential are provided by a wide range of factors, but most typically they involve, cool damp shade, flushing by springs or occasional flooding, or less frequently, flushed steep slopes, damp, shady narrow cliff ledges, trampling of grassy paths, or other forms of moderate disturbance.

Fermanagh occurrence

While it is widespread throughout most of Fermanagh, having been recorded in 233 tetrads, 44.1% of those in the VC, Yellow Pimpernel prefers fertile or base-rich soils of moderately acid to neutral pH levels and is, therefore, only occasional in limestone areas of the county. Having said this, the tetrad map shows it widely dispersed around most of the VC, avoiding strongly acid peat and the driest rocky ground.

Reproduction

The very attractive, solitary, long-stalked, yellow, star-like flowers are often quite profusely produced and a succession of them appears between early May and mid-September. However, seed production is generally sparse and reproduction relies heavily on vegetative spread by nodal rooting of the prostrate shoots, which can be up to 45 cm in length (Salisbury 1942). The frequent low levels of seed production by the species is odd, given that the flowers, while without nectar, offer pollen and attract flies, bees and other insect visitors which could pollinate them. They are also said to be homogamous (ie the male and female parts mature simultaneously) and self-fertile (ie autogamous), which also ought to ensure a good seed set (Vogel 1978, p. 91; Fitter 1987). The fruit is a small, globular capsule that splits to release the few, angular seeds (Melderis & Bangerter 1955).

Despite the observed limited seed production, a lack of any specialised dispersal mechanism and presumably resultant poor transport, the ease with which the stems root and vegetatively produce clonal patches, often allows L. nemorum to become locally abundant in damp to marshy grassy vegetation.

Ecological effect of mowing and grazing

Yellow Pimpernel does not survive mowing (Hansen & Stahl 1993) and, similarly, it cannot tolerate much grazing (Sinker et al. 1985). The small scale of the plant, together with the open nature of many of its habitats, makes browsing depredation unlikely in any case. Gardeners have noted that unlike other cultivated members of the Primula family, L. nemorum does not suffer the attentions of rabbits. This suggests that, like Anagallis arvensis (Scarlet Pimpernel), it probably contains sufficient saponins to make it unpalatable, or possibly even toxic to some herbivores (Cooper & Johnson 1998; Thomas 2004).

British and Irish occurrence

The New Atlas distribution map displays L. nemorum as being widespread throughout most of B & I, although less common in C Ireland and absent in Britain from much of the east coast and a considerable area of the E Midlands (Preston et al. 2002). Comparison of the records for the species in the 1962 and 2002 BSBI Atlas surveys shows L. nemorum has suffered a widespread decline in S England over the years, with a calculated Change Index of -0.46. Destruction of deciduous woodland over this period and its replacement with coniferous plantation has created dense shade habitat conditions that are totally unsuitable for Yellow Pimpernel.

Fossil history

The fossil record for both L. nemorum and L. nummularia (Creeping-Jenny) is very poor in B & I. Seeds of one or other have been identified from only one site in Kent dating from the relatively recent Zone VIIb of the current interglacial period (Godwin 1975, p. 308). This does not give any indication as to their means of transport to these islands, or the antiquity of either of these assumed native species.

European occurrence

Beyond our shores, L. nemorum is very much confined to W & C Europe. It is absent from Iceland and from areas of Scandinavia north of 60°N. Interestingly, although the species is absent from Shetland, it has been recorded on one sandy and gravelly lake shore in the Faeroe Isles, though how it got there is problematical (Ostenfeld & Grontved 1934). The remote population on the Azores is distinguished as subsp. azorica (Horn.) Palh. (Hulten & Fries 1986, Map 1476).

Medicinal uses

Yellow Pimpernel had or has very few folk medicinal uses, although the yellow flowers were boiled in County Cavan as a cure for gallstones and there is some suggestion that it may have shared the soporific effect of its relative Primula veris (Cowslip) (Allen & Hatfield 2004).

Threats

None.

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