Scleranthus annuus, commonly known as knawel or German knotgrass, is a plant species with small green leaves and tiny white flowers. Some synonyms for this plant include Scleranthus annuus var. annuus, Scleranthus annuus subsp. annuus, and Scleranthus annuus f. annuus. Other common names for this plant include mat weed and lawn pearlwort. This plant is often used as a ground cover and is known for its ability to tolerate compacted soil and heavy foot traffic. It is also a common weed in lawns and gardens, where it can be difficult to control.