Creeping knotweed
Polygonum prostratum (persicaria prostrata)

Decumbent herb, often with a woody rootstock, ± densely antrorsely hairy, occasionally with scattered stalked glandular hairs too.

Leaves narrow-ovate, 1–4 cm long, 3–10 mm wide, with antrorse hairs scattered on surface or restricted to veins and margins, occasionally sessile glands on lower surface too; petiole 0–3 mm long; ocrea with cilia 1–2 mm long, limb lobed and toothed.

Spikes short-cylindrical, dense, 0.6–4 cm long, 4–7 mm diam. Perianth segments 1.8–2.5 mm long, elongating to 3.2 mm in fruit.

Achene lenticular, 1.5–2.0 mm long, 1.2–1.3 mm diam., dark brown to black.