Scleranthus annuus aka German Knotweed

Scleranthus annuus, or annual knawel, belongs to the pink family, Caryophyllaceae. Other names include German knotweed and German moss. Its native range includes Macaronesia, Europe, North Africa, and parts of Asia. It reaches central Siberia, Iran, and the Arabian Peninsula. It is native to Britain and Ireland, too. Introduced plants now grow across much of the United States and Canada. Kew records it as an annual or biennial in temperate regions.

This small herb grows about 0.17–0.42 feet (0.05–0.13 metres) tall. Its many branches spread along the ground or turn upward. Together, they can make a dense mat of low growth. The green stems lack scent and have few or no hairs. North Carolina State describes it as a winter annual. Seeds sprout in winter, and plants grow during warm spells. They flower in early spring, then die by early summer. Seeds carry the plant into its next life cycle.

The leaves are green, simple, and narrow, with smooth edges. Some curve slightly, and each ends in a stiff point. Leaves reach about 0.08 feet (0.025 metres) long. They grow in opposite pairs, joined at their bases. Each pair sits at right angles to its neighbours. Close spacing can make the leaves look whorled. This packed leaf pattern helps give the plant its dense look.

Small, star-shaped flowers crowd the ends of forked branches. Each flower measures about 0.01 feet (0.003 metres) across. Green sepals with white margins provide the petal-like parts. The flowers have two to ten yellow stamens. Their pointed parts can feel somewhat prickly to touch. Each egg-shaped fruit forms a capsule holding one seed. The flowers are small and do not make a showy display.

Annual knawel grows in fields, lawns, and disturbed ground. It favours sand or gravel but also grows in loam. Good drainage suits it, though it tolerates moist sites. It withstands drought and grows in sun or partial shade. In gardens, its documented problem is its weedy growth. Its spreading form can occupy space within a lawn. Records note past use in herbal medicine. That history alone does not establish safe use as medicine or food.