Medium to tall, greyish, hairless, stoloniferous plant. Stems little branched, ridged, hollow and often constricted at the nodes. Basal leaves 1 to 2 pinnate with oval lobed leaflets. Upper leaves pinnate with narrower leaflets, untoothed, with sheathing long hollow stalks. Flowers white or pink 3 mm in small umbels with only 2 to 4 thickened rays. Generally without bracts.

All umbels terminal; fruits without stalks, forming a globular cluster when ripe; leaves with petioles longer than the divided part; stems hollow and very thin-walled.

A series of photos of the plant in its habitat, with details of flower heads and/or fruits, stems and leaves (RPR)

Shallow water and marshy habitats on fertile soils.

Flowers June to September.

Perennial.

Widespread and fairly frequent in Britain from Yorkshire southwards, though less frequent in the south west.

Scarce and declining in Leicestershire and Rutland. In the Flora of Leicestershire (Primavesi and Evans 1988) it was found in 45 of the 617 tetrads, and in the Flora of Rutland (Messenger 1971) in 2 tetrads.

In the current Checklist (Jeeves, 2011) it is listed as Native; possibly scarce; it has declined sharply and now known from about 10 localities, almost all in the Soar valley.

It is listed on the current VC55 Rare Plant Register (Hall and Woodward 2022) because of its threat-level