Botanical name: Polygonum heterophyllum
Also known as: Hogweed, Knotweed, Prostrate Knotweed.
Wireweed is a hairless, ground-hugging or sprawling, annual or perennial herb with small oval leaves usually 5-12 mm long. At the base of each leaf is a white to silvery sheath around the stem. In the leaf axils there are small clusters of pink-tinged flowers 2-3 mm long. Each flower is 5-lobed and has 7 or 8 stamens and 3 styles. The fruits are small, 3-angled and enclosed in the withered flower. The stems are slender, up to 1 m long, wiry and many branched.
Native to Europe, Wireweed is a common weed of pastures, roadsides and waste land. Flowering occurs in autumn and spring.
STEM AND LEAVES
The stem is prostrate (occasionally ascending), sprawling, up to 1000 mm long, wiry, stiff, solid, round or fluted with lengthwise grooves. Many branches at the base and along their length. Hairless. May form dense mats. Often reddish.
The leaves grow singly and are spear shaped with a pointed tip, 10-15 mm long on a short stalk. Hairless. A membranous sheath surrounds the base of the leaf and stem. Later leaves are similar but larger.
FLOWERS AND FRUITS
Flowers are single or in clusters of 1-5 in leaf axils on short stalks.
Nut. Triangular pyramid, dull brown to reddish black with dots and streaks, finely granular, 2-2.5 mm long. Usually inside the persistent flower parts. Fruit dimension and shape are used to determine separate different subspecies and varieties (Meerts et al., 1990).
REPRODUCTION AND DISPERSAL
This species reproduces by seed
Ribwort (Plantago lanceolata) is very similar as a seedling. Its cotyledon is narrower and longer, its first leaf is usually hairy and has a well defined median groove, lengthwise veins and has no sheathing membrane at the base of the leaf.
Bucks Horn Plantain (Plantago coronopus) is similar as a seedling until it produces its lobed, later, leaves. It also lacks the sheathing membrane (ochrea) at the base of the leaf.