Tribonanthes purpurea This is a tiny flannel flower which grows in moss on granite rocks. It is listed as a Threatened plant and grows in only a few locations. The flower is about 1cm tall, the leaves growing to 3-4cm. It is a very hard plant to locate and find even when you know where it is. More photos in first comment
Native to Central America and Mexico, this species is now pantropical due to its use as a ground cover. Names include Inch Plant, Wandering Jew and Amor de Hombre.