Ferns are a group of about 20,000 species of plants (of which about 10,000 are living) in the division Pteridophyta. Unlike bryophytes, ferns have xylem and phloem, which makes them vascular plants.
|Polystichum setiferum showing unrolling young frond|
Most ferns belong to the Class Leptosporangiata (or Pteridopsida). This includes most of those you see in gardens and woods. The horsetails belong to another class, the Equisetopsida, which was extremely important in the Carboniferous period. Only one genus survives. The other classes of fern are also quite small today.
Ferns do not have waxes or special cells on their surface that keep water from evaporating. They have roots, stems, leaves. Their stems may form runners, called stolons above the ground, or rhizomes below ground. The leaves are green and large, and may bear spores on the underside. Some ferns can grow large in moist places. They can survive in more places than moss, but not so many as flowering plants.
During the Carboniferous period – from 350 million years ago – ferns lived everywhere on land. Horsetails grew up to 30 metres. There were huge forests of ferns and mosses, full of giant insects. Today, there are not so many large ferns.
- Stein W.E. et al 2007. Giant cladoxylopsid trees resolve the enigma of the Earth's earliest forest stumps at Gilboa. Nature 446, 904-907. 
- Also known as Filicophyta
- Taylor, Thomas N. & Edith L. Taylor. 1993. The biology and evolution of fossil plants. Englewood Cliffs, NJ: Prentice Hall. pp. 303–305. ISBN 0-13-651589-4.
- Pryer, Kathleen M., Harald Schneider, Alan R. Smith, Raymond Cranfill, Paul G. Wolf, Jeffrey S. Hunt and Sedonia D. Sipes. 2001. Horsetails and ferns are a monophyletic group and the closest living relatives to seed plants. Nature 409: 618-622 (abstract here).
- Pryer, Kathleen M., Eric Schuettpelz, Paul G. Wolf, Harald Schneider, Alan R. Smith and Raymond Cranfill. 2004. Phylogeny and evolution of ferns (monilophytes) with a focus on the early leptosporangiate divergences. American Journal of Botany 91:1582-1598 (online abstract here).
- Moran, Robbin C. 2004. A natural history of ferns. Portland, OR: Timber Press. ISBN 0-88192-667-1.
- Lord, Thomas R. 2006. Ferns and fern allies of Pennsylvania. Indiana, PA: Pinelands Press. 
- Smith A.R., K.M. Pryer, E. Schuettpelz, P. Korall, H. Schneider & P.G. Wolf. 2006. A classification for extant ferns. Taxon 55(3):705–731.online available
Tree fern Spores San Diego
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