Lysimachia nummularia L., Creeping-Jenny

Account Summary

Growth form and preferred habitats

This evergreen, mat-forming, fast creeping perennial is common and easily recognised, but both the wild type and a golden-leaved form (var. aurea) of it are quite commonly cultivated (usually by alpine gardeners or in hanging baskets), flowering from May to September (R.G. Woods, in: Perry & Ellis 1994). They are often invasive in the deep, fertile soil of a damp garden situation, require cutting back after flowering; they sometimes escape or are dumped with garden waste and become naturalised, confusing the native distribution to some extent (Grey-Wilson 1989). However, it would seem likely, that following the pattern of the southern portion of its British range and throughout Ireland, it is probably native in almost all of its large number of Fermanagh stations. The typical habitats it occupies in the VC are damp, often shady places by lakes, rivers and in woods, rather than in more disturbed sites or close to habitation, as might be expected of a garden escape.

Fermanagh occurrence

Creeping-Jenny is quite commonly found in damp, open ground in Fermanagh. It has been recorded in 118 tetrads, 22.4% of those in the VC. As the tetrad distribution map indicates, it is mainly but not exclusively found around the shores of Upper and Lower Lough Erne. The author(s) of the Revised Typescript Flora (essentially R.D. Meikle) very definitely regarded L. nummularia as a, "characteristic plant of the Erne basin". Having said this, in some sites the status of the species must remain questionable and, very possibly, at least some of the Fermanagh records are garden escapes.

Species status in Britain and Ireland

Stace (1997) describes the distribution of L. nummularia as follows (some abbreviations expanded but otherwise quoted verbatim), "Native; damp places, often in shade; throughout most of B & I north to C Scotland, but a naturalised garden escape in many localities, especially in the north." The 1962 BSBI Atlas accepted the vast majority of B & I records as native, with only a tiny minority of 'recorded introductions' in the N & W of Britain and in NW Ireland (Walters & Perring 1962). That said, the main British distribution lies south of a line between Hartlepool and Heysham, thinning markedly northwards. County Floras of Durham (VC 66) and Cumbria (VCs 69, 70 and parts of 60 & 65), indicate that L. nummularia is somewhat more widespread in these areas than previously thought and, in these areas, it represents a mixture of native and naturalised populations (Graham 1988; Halliday 1997).

Praeger (1934i) assembled some of the facts regarding the Irish distribution and, while acknowledging that L. nummularia is commonly cultivated in gardens, he argued strongly that the species should be considered indigenous.

In his Botanist in Ireland, Praeger (1934i, paragraph 76) argued that the species should be considered indigenous in at least some of its stations. He maintained that, "the flora becomes more and more aboriginal as the soil becomes unsuitable for agricultural operations, as on bogs, marshes and mountains".

In a paper on the standing of certain plants in Ireland (Praeger 1934b), he wrote in relation to this species, "lake shores and marshes are habitats where the alien element in the flora is at a minimum", a statement with which the current author simply could not agree. However, as Webb (1985) very sensibly pointed out, a plant simply, "looking wild" and growing amongst undoubtedly native associates, does not necessarily qualify as indigenous itself by so doing. It should be realised that Praeger had a strong penchant for plumping for species as indigenous which others considered doubtful (Praeger 1934i & 1937b).

Reproduction

Creeping-Jenny produces almost no seed anywhere in these islands, yet it is a remarkably widespread species. It frequently occupies waterside habitats that provide it with an obvious means of rapid seed and vegetative dispersal. Even without water transport, the plant can spread locally to form extensive patches by means of rapid, prostrate stem growth and rooting at nodes. Taken together these methods of increase should ring alarm bells and hint at some form of introduction. Further investigation is required to clarify the status issue but, as the situation stands, RHN and the current author (RSF) feel the Fermanagh lakeside and woodland stations of L. nummularia are best considered only 'probably native'.

The basis of the observed high degree of seed sterility in L. nummularia was investigated throughout its European range by Bittrich & Kadereit (1988), examining both live and herbarium material. Meiotic irregularities were common (ie failure of chromosome pairing), resulting in a high percentage of non-viable pollen and pollen grains of unequal chromosome number. Rarely, however, some individuals were capable of seed set, so sterility is not total. In many populations, the self-incompatibility of the species and the reliance on vegetative clonal reproduction has led to increasing levels of sterility.

Despite the above, the frequency of fertile individuals is comparatively high in SE Europe, which probably served as an ice-free refugium for the species during glacial periods. It seems likely that during the spread of L. nummularia into northern latitudes after the glaciers retreated, only a few genotypes may have been involved, perhaps migrating mainly by vegetative means, which would lead in time to a degeneration of the sexual reproduction system of the plant.

European and world occurrence

L. nummularia is present across most of middle latitude Europe, northwards into S Scandinavia and stretching east to the Caucasus. The distribution also thins southwards into the Iberian and Balkan peninsulas. On account of its garden cultivation, it is widely introduced and naturalised beyond its native range and is quite frequent and widely scattered in eastern N America and present also in New Zealand (Hultén & Fries 1986, Map 1478).

Threats

None.

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