Annual knawel is an annual in the pink family ( Caryophyllaceae) and native to Europe, Asia, and North Africa. Also known as German knot weed, it has spread throughout the temperate world and is widespread in the eastern half of the US and the West Coast where it can be found growing in disturbed areas including gardens, lawns, roadsides, and meadows. It prefers full sun and dry, well-drained soil. Because it is low growing and resembles grass when it first germinates, it may be inconspicuous. The generic name, Scleranthus comes from the Greek word skleros meaning hard, and anthos meaning flowers, and refers to the hard covering on the fruit produced by the receptacle of the flower.
Annual knawel is a sprawling freely branching plant with spreading stems than can form dense mats. The bright green leaves clasp the stem and are linear, opposite, and needle-like with stiff, sharp points. The green flowers lack petals and are carried in dense clusters in the leaf axils. They bloom from June to September and are followed by small dry one seeded fruits (achenes) that remain viable in the soil for several years. The plants are anchored by a fibrous taproot.
Remove plants from the garden with a hoe or by pulling before seed set. When the weed becomes established in a lawn a selective broadleaf herbicide in summer or preemergent herbicide fall or in early spring before plants appear may be useful.