Perennial, speading by seed which are carried by the wind from the upright seed
pods, as they split lengthwise and curl open - although most fall close to the parent plant. The leaves are finely toothed with no hairs, arranged alternately near the top of the stem and opposite lower down. The round stem is hairless, but no has raised lines and dies away in the late autumn. The plant overwinters as leafy buds at ground level and start into growth early in the spring (bottom picture). Some of the buds grow sideways on the surface and take root to form a larger clump in subsequent years.
The flowers open from June to August - small pale pink at the tip of a slender ovary. The four petals have a deep notch and the stigma has four lobes. After maturity the fruit splits open to release the pappus which carries the seed.
The height can be up to 60cm in good growing conditions, but is usually about 35cm.
The plants ale easily uprooted and the adventitious roots will not regrow provided the growth point is removed. The stem snaps easily at soil level and regrows with 3 or 4 new shoots if left behind. When hoeing ensure that the blade cuts below soil level. Any uprooted or severed plants should not be left lying around as there will be enough sap to open mature seedheads to release the seed.
Other similar Willowherbs have the same growth habits and should be treated with the same distain, eg. E. ciliatum, American Willowherb a native of North America, has fine hairs on the stems, but not on the leaves - now established in the British Isles. E. parviflorum, Small-flowered or Hoary Willowherb has hairy leaves and stems.