section_path: Evolution/Evolutionary history
section_name: Evolutionary history
paragraph_text: Evolutionary history
  
  The ancestors of land plants evolved in water. An algal scum formed on the land 1,200 million years ago, but it was not until the Ordovician, around 450 million years ago, that the first land plants appeared, with a level of organisation like that of bryophytes. However, fossils of organisms with a flattened thallus in Precambrian rocks suggest that multicellular freshwater eukaryotes existed over 1000 mya.
  
  Primitive land plants began to diversify in the late Silurian, around 420 million years ago. Bryophytes, club mosses, and ferns then appear in the fossil record. Early plant anatomy is preserved in cellular detail in an early Devonian fossil assemblage from the Rhynie chert. These early plants were preserved by being petrified in chert formed in silica-rich volcanic hot springs.
  
  By the end of the Devonian, most of the basic features of plants today were present, including roots, leaves and secondary wood in trees such as Archaeopteris. The Carboniferous Period saw the development of forests in swampy environments dominated by clubmosses and horsetails, including some as large as trees, and the appearance of early gymnosperms, the first seed plants. The Permo-Triassic extinction event radically changed the structures of communities. This may have set the scene for the evolution of flowering plants in the Triassic (~ 200 million years ago), with an adaptive radiation in the Cretaceous so rapid that Darwin called it an " abominable mystery ". Conifers diversified from the Late Triassic onwards, and became a dominant part of floras in the Jurassic.