| Ferns first appear in the Devonian and are common in the Cretaceous rocks of the Arctic, where, together with sphenophytes such as Equisetites, they formed most of the groundcover biomass. These spore-producing plants typically have fronds with a central rachis from which side branches (pinnae) bear individual leaves (pinnules). There may be several orders of branching. Young fronds unroll from 'fiddle heads' or 'croziers' - a phenomenon known as 'circinate vernation' (below). Some ferns are aquatic (e.g. Hausmannia), some are epiphytes, some are climbers, some form groundcover (e.g. Birisia, Arctopteris) and some attain tree stature. |
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