Flower:

Flowers are borne singly or a few at the tips of branching stems, or on a stalk arising from a leaf axil. Individual flowers are less than ¼ inch across with 4 rounded green sepals usually alternating with 4 white petals smaller than the sepals, though the petals may be absent altogether and rarely a plant may have some flowers with 5 petals and sepals. In the center is a yellowish-green ovary with 4 styles at the tip surrounded by 4 pale stamens. All parts are hairless. After pollination, the flower becomes nodding and the sepals close tightly around the flower.

Leaves and stems:

Leaves are about 1 mm wide, hairless, toothless, stalkless, linear, often with a minute, bristle-like tip and are sometimes somewhat fleshy. Basal leaves are longest, to 2/3 inch long and often arranged in a rosette; stem leaves are shorter and opposite though may appear whorled due to leaf clumps in the axils. Stems are green, hairless, usually much branched, multiple from the base, ascending or more often prostrate, rooting at the nodes and forming mats.

Fruit:

Fruit is a capsule with 4 triangular teeth at the tip. As fruit matures, the sepals become spreading and the capsule turns upright, the teeth spreading open to release the numerous tiny, blackish-brown seeds.

Notes:

Bird's-eye Pearlwort is an introduced species in Minnesota that occasionally escapes cultivation. Its origin is murky, some references noting it is European or Eurasian and others that it's native to parts of North America. In either case, it is not commonly found in the wild, but more in areas of human disturbance such as pavement cracks, roadsides, lawns, gardens, rocks and shores. It is most easily distinguished by the mat-forming growth, overall hairlessness, strap-shaped leaves, 4-parted flowers with petals usually rather smaller than the sepals (or absent altogether), and the upright capsule with 4 teeth/lobes at the tip. By comparison, the related (and very rare) Knotty Pearlwort (Sagina nodosa), has few stem leaves and 5-petaled flowers with petals much larger than the sepals.