This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Introduced. Annual. Propagates by seeds. Time of bloom: May to August. Seed-time: June to September. Range: Throughout North America except the far North. Habitat: Dry soil; waste places.
A very slender, much-branched, and spreading little plant. Not an aggressive weed but merely doing its best to cover dry and sterile soil, that is unsuited to plants of more worth. Stems two to eight inches high, light green, and rough-hairy. Leaves opposite, sessile, ovate, acute, hardly more than a quarter-inch long. Flowers many, very small, white, in leafy, cymose panicles; sepals five, lance-shaped, pointed, bristly on the back, about as long as the petals, which are also five, oblong or obovate. Stamens ten, with lilac anthers. Styles three. The capsule is one-celled, shaped like a tiny flask, opening at the top by six outward-curving teeth. Seeds many, very small, compressed, rough. (Fig. 89.)
Fig. 89. -Thyme-leaved Sandwort (Arenaria serpyllifolia). X 1/3.
Ground preferred by Sandwort is not fit to grow much else, until it has been enriched and supplied with humus, which will enable it to retain moisture; better plants will then soon take the place of the weed.