Sea Purslane,, or Sesuvium portulacastrum.

This plant will spread several feet in all directions over a period of a few months. They resist burial very well by retaining the sand with its stems which cover the sand surface. The stem color varies depending on the availability of nutrients, the temperature, and the water conditions. Sea Purslane is a very decorative plant with small purple flowers and stem colors that range between green, orange and red. It is a definite keeper for erosion control.