This is an annual plant ubiquitous in disturbed ground, arable fields and even appearing as a weed in gardens. It is widespread around Scotland, though not in the far North, with a similar distribution to Redshank (Persicaria maculosa). The name Knotgrass refers to the swelling ‘knots’ that occur at the leaf nodes. Though seen almost everywhere it is often overlooked as an insignificant weed.
The stems are many branching and low growing or turning upright, and hairless. The leaves are spirally arranged around the stem, and between 20 and 50mm in length. They are spear shaped, with pointed tips and unbroken edges. In colour they tend towards a greyish green. The leaves have short stalks, narrowing as they met the stalk.
Flowers grow in loose clusters of 2 to 6, or singly from the base all along the stem and are small greenish perianths of 5 lobes, turning to pink or white at the edges. Each flower is about 2 – 3mm long and looks like a short tube at the base, splaying out slightly as the lobes separate. The flowers are covered in papery sheaths, from which they emerge as they open.
5 to 8 short stamens and 2 stigmas can be seen in the middle of the perianth.
The fruit is nut-like, 3 sided, and it is hidden in the lobes of the dried flower.