Very early in the spring, before the trees begin to leaf out, the mosses  do much of their growing for the year.  Mosses are related to the most ancient of land plants. They have no seeds or flowers, and they are absolutely dependent on free water for sexual reproduction. Unlike in seed plants, where the male reproductive cells are transported as part of the pollen grain, in the mosses, the male reproductive cells are swimming sperm that must be able to swim from one plant to another.  If they are successful, and fertilization happens, the plant forms the characteristic "pixie cap" structure, called a sporangium. Meiosis happens inside this structure and the tiny spores that are produced are spread by wind to start new plants. 

If you have arrived at this page from a QR code on the trail, you should be able to see some of the sporangia on the rocks at about eye level (if you are around 5ft 9 or so). Besides the green mosses, you might notice some greyish green plants of similar size.  These are lichens, with are part algae and part fungi.