Euphorbia peplus L., Petty Spurge

Introduction, archaeophyte, occasional. European southern-temperate, but widely naturalised and now circumpolar.

1882; Stewart, S.A.; Co Fermanagh.

April to December.

Petty Spurge is a little, bushy, ruderal summer-annual, 15-30 cm tall, with a relatively large, diffuse inflorescence of small flowers in umbels, usually with three main branches. The glands in the flowers are crescent-shaped with long, slender points. The fruit capsule is slightly keeled or winged, having two dorsal ridges on each of the three carpel valves (Sell & Murrell 2009; Parnell & Curtis 2012). Petty Spurge is a plant of warm, well-drained, fertile, disturbed or cultivated soils, including gravel, shingle, stony ground and pavement cracks. Although it can survive in full sun if watered or rained upon at intervals, as it is shallow-rooted, plants generally perform best in semi-shaded sites where the substrate is less likely to dry out entirely.

Like the smaller E. exigua, whose fruits are smooth and not keeled, it was included in the list of 41 species previously assumed to be native in Britain that Webb (1985) considered were probable introductions by man, and whose traditional status required further study. In response to this clarion call, the New Atlas editors and Preston et al. (2004) reviewed its status and now recognise E. peplus as an ancient or pre-1500 introduction.

In Fermanagh, Petty Spurge is only an occasional, widely scattered lowland species of gardens and urban disturbed ground. It has been recorded in a total of 29 tetrads, 5.5% of those in the VC. In view of its diminutive, useless and weedy nature, this is obviously an accidentally imported species, most likely arriving from Mediterranean Europe either as a crop seed contaminant, or with soil on the roots of other more desirable imports, or carried on the feet or on the coats of transported animals, or with other cargo. E. peplus has also been transported very much further afield, to S Africa, Japan, N and S America, Australia and New Zealand, so that nowadays the species has a discontinuous circumpolar distribution in the N Hemisphere and in wider temperate and sub-tropical regions of the world (Hultén & Fries 1986, Map 1284). In areas outside its native range, E. peplus becomes naturalised and is often invasive, although on account of its small size, it is rarely or never a serious weed.

In B & I, the distribution of E. peplus, although widespread and common, has a southern and eastern preponderance, becoming more coastal in the N & W of both islands. This suggests a winter low-temperature limitation exists, a feature consistent with the supposed Mediterranean centre of origin of the species. The B & I distribution appears stable, with no noticeable change in presence during the 40 years between the two BSBI Atlases (Perring & Walters 1962; Preston et al. 2002).

Petty Spurge can germinate and grow all year round provided water is available. Plants grow rapidly and reach maturity in 12-14 weeks. Although it normally develops only a small, bushy individual about 20 cm tall, the seed production of E. peplus plants is high with a mean value around 260 per plant. Pollination of the flowers involves small flies, although selfing may also be possible (Fitter 1987). Seeds possess a small attached edible elaiosome oil-body that attracts ants which help them to disperse and avoid seed predation (Ross-Craig, Part XXVI, Plate 41: 1967-70). Since seed can survive for over 20 years (perhaps 50-100 years) in the soil, the species is very well protected from local extinction (Thompson et al. 1997). Seedlings appear between May and August and flowering occurs from July to November (Salisbury 1964, p. 315).