It is hard to distinguish from other buttercups, but the narrow oval leaves without lobes give Lesser Spearwort away. It grows beside streams and in wet meadows, often with its roots standing in the water, and can be found throughout Scotland.
Stems are angled upwards, sometimes creeping along the ground and sending down roots. The stem is grooved, reddish and sometimes with sparse hairs but not always. Leaves grow in a spiral arrangement up the stem, and are narrow, lanceolate, from 10 to 50mm long with a tapered base, and either slightly toothed at the edge or smooth. Lower leaves have long stalks but upper leaves are sessile.
Flowers grow in singles or 2 or 3, on branched stalks at the tip of the stem. They are pale and glossy yellow and look very like other buttercups, having 5 broad and rounded petals arranged in a loose cup shape, supported by 5 shorter green sepals which droop downwards when the flower is open. The flower is up to 2cm across. Numerous yellow stamens, easily 30 or more, fill the centre of the corolla, and numerous ovaries, each with its own stigma, ripen into a globular cluster of brown seed pods after the petals have fallen.
Like other Buttercups, Lesser Spearwort is acrid and the leaves or roots, if grinded with salt, can blister the skin. It was used to treat the sores of Bubonic plague in the 16th century.
Greater Spearwort is a larger plant, over a metre tall with larger flowers, but is very rarely seen in Scotland.