Sphagnum such gemmae. Peat moss can be distinguished from other moss species by its unique branch clusters. The plant and stem color, the shape of the branch and stem leaves, and the shape of the green cells are all characteristics used to identify peat moss to species. "Sphagnum" taxonomy has been very contentious since the early 1900s; most species require microscopic dissection to be identified. In the field, most "Sphagnum" species can be identified to one of four major sections of the genus—classification and descriptions follow Andrus 2007 (Flora North America): The reciprocal monophyly of these sections and two other minor
Moss Antarctica and Russia, and a case is put forwards for Carboniferous mosses. It has further been claimed that tube-like fossils from the Silurian are the macerated remains of moss calyptræ. Mosses also appear to evolve 2–3 times slower than ferns, gymnosperms and angiosperms. Recent research show that ancient moss could explain why the Ordovician ice ages occurred. When the ancestors of today's moss started to spread on land 470 million years ago, they absorbed CO from the atmosphere and extracted minerals by secreting organic acids that dissolved the rocks they were growing on. These chemically altered rocks in turn reacted