Spergularia salina, Salt Marsh Sandspurry
"Leaves little mucronate, fleshy; stipules broadly deltoid to ovate; stamens 2-5"
(Note the two stamens in the photo at left.)
Status uncertain; coastal plain only, per the checklist, but this plant was found in the Piedmont.

Spergularia rubra, Purple Sandspurry
"Leaves mucronate; stipules lanceolate to narrow-deltoid; stamens 6-10"
Alien; coastal plain only.

Sources: The Flora of Delaware, Herbaceous Plants of Maryland.