Sagina procumbens aka Birdseye Pearlwort

Sagina procumbens is a low herb in the carnation family, Caryophyllaceae. Its names include pearlwort, matted pearlwort, and procumbent pearlwort. It is native to Macaronesia, Europe, Siberia, the Mediterranean, and Iran. The RHS confirms that it is native to Britain and Ireland too. It also grows in Greenland and cooler parts of the Americas. It forms green mats that look much like moss. This perennial lives a short time. It can also grow as an annual, living one year.

Plants reach about 0.5 feet (0.15 metres) tall. They spread along the ground. One or more smooth, bright green stems grow from a leaf rosette. Narrow leaves grow in pairs along these stems. Each pair joins at its base and clasps the stem. The stem swells a little at these points. The thin, needle-like leaves have smooth edges. A shallow taproot splits into many small roots beneath the mat.

Flowers grow at stem tips, alone or in small groups called cymes. Each open flower spans about 0.02 feet (0.006 metres). Four green sepals surround up to four small white petals. Some flowers have no petals. Others have petals that hardly grow. Each flower also has four stamens. The detailed account gives mid- to late spring as bloom time. Bloom lasts about a month. The source also lists fall. White seed cases, called capsules, follow the flowers. These have thin walls and four blunt teeth around their tops. Each holds several tiny, dark seeds with a fine surface texture. Wind can carry the seeds away.

Pearlwort grows best in cool, moist sites where water drains well. It grows in light shade or full sun. Sandy and rocky soils suit it. Clay and loam also appear among the soils it accepts. Most leaf growth takes place in cool, damp spring weather. NC State lists USDA hardiness zones 1 through 6. Plants spread fast as seeds sprout and form small groups. They cope with some foot traffic, but not heavy use.

Gardeners grow it in rock gardens and gaps between paving stones. Its fine leaves form low ground cover near paths. Yet its large seed crop can make it a problem weed. Stopping seed set helps curb spread where it is not wanted. Better drainage can also help it last less long in such sites. NC State lists its care needs as high. That source reports no known insect pests or diseases. The supplied evidence does not show whether it is safe to eat or toxic.