Peperomia pellucida, also known as "rau càng cua" in Vietnamese, is a common herb that grows abundantly in the moist, shaded areas of the country side.  This herb has very tender stems that seem almost translucent and the leaves are heart-shaped and shiny.  The entire plant is edible.  It is most often used in salads with a vinegar dressing.  

In the warm regions, this herb will grow all year long.  In nontropical places, the plant will drop seeds where they will remain dormant until the following warm season.  They produce lots of tiny black seeds, but can also be grown by propagation.