Cancer Weed

Foodplant / parasite
telium of Melampsora euphorbiae parasitises live stem of Euphorbia peplus
Other: major host/prey

In Great Britain and/or Ireland:
Foodplant / parasite
sporangium of Peronospora euphorbiae parasitises live leaf of Euphorbia peplus

Foodplant / parasite
cleistothecium of Podosphaera euphorbiae parasitises Euphorbia peplus

Herbs, ephemeral, erect or ascending, 10-30 cm tall. Taproot 1-2 mm thick. Stems single or branched near base, ca. 2 mm thick, ascending. Leaves alternate, mostly uniform in size; stipules absent; scale-leaves absent; petiole 1-3 mm or almost absent; leaf blade obovate to spoon-shaped, (0.5-)1.5-4 × (0.4-)0.7-1.8 cm, pale green, usually glabrous; base cuneate below, truncate or cordate above, margin entire [or finely serrulate above middle], apex rounded; midrib inconspicuous. Inflorescence a terminal pseudumbel, rays irregularly branched, lateral branches few; primary involucral leaves 3 or 4, similar to normal leaves; primary rays 3 or 4, short; cyathophylls 2, similar to normal leaves. Cyathium subsessile; involucre cuplike, ca. 1 × 1 mm, lobes rounded, ciliate; glands 4, yellow-green, crescent-shaped, apex 2-horned, horns ± threadlike. Male flowers many, usually not exserted from involucre. Female flower: ovary pedicel 2-3.5 mm, exserted from cup; ovary trigonous, smooth, glabrous; styles free; style arms 2-lobed. Capsule oblong-ovoid, 3-lobed, 2-2.5 mm, smooth with 2 narrow wings along each keel, glabrous. Seeds ovoid-angulate, 1.2-1.3 × 0.7-0.8 mm, gray or gray-white, each surface with 2 or 3 micropores; caruncle present, peltate, yellow-white, sessile. Fl. and fr. Feb-Oct.

Weed of disturbed areas, roadsides, gardens, grasslands. Fujian (Fuzhou, Xiamen), Guangxi (Nanning), Hong Kong, Taiwan (Taibei, Taizhong), Yunnan (Kunming) [N Africa, America, S Europe, Pacific islands].

Esula peplus (Linnaeus) Haworth; Tithymalus peplus (Linnaeus) Gaertner.

Tender glabrous annual herb up to 30 cm

Native of Europe and E Asia

Euphorbia peplus (petty spurge, radium weed, cancer weed, or milkweed), is a species of Euphorbia, native to most of Europe, northern Africa and western Asia, where it typically grows in cultivated arable land, gardens and other disturbed land.

Outside of its native range it is very widely naturalised and often invasive, including in Australia, New Zealand, North America and other countries in temperate and sub-tropical regions.