Unknown cross-leaved plant

Unknown cross-leaved plant

Observation - Unknown cross-leaved plant - UK and Ireland. Description: This plant was carpeting an area of shingle at the edge of a flooded gravel pit. A closer look revealed very small four-petalled white flowers.

This plant was carpeting an area of shingle at the edge of a flooded gravel pit. A closer look revealed very small four-petalled white flowers.