The Cyatheaceae are the scaly tree fern family and include the world's tallest tree ferns, which reach heights up to 20 m. They are also very ancient plants, appearing in the fossil record in the late Jurassic, though the modern genera likely appeared in the Cenozoic. Cyatheaceae are the largest family of tree ferns, including about 500 species. Cyatheaceae and Dicksoniaceae, together with Metaxyaceae and Cibotiaceae, are a monophyletic group and constitute the "core tree ferns". Cyatheaceae are leptosporangiate ferns, the most familiar group of monilophytes.
The Cyatheaceae usually have a single, erect trunk-like rhizome (stem). Their fronds (leaves) are also very large, some of the largest in the plant kingdom. Some species have fronds reaching 3–4 m in length, and have a final crown width of some 6 m. The fronds are circinate before unfolding and usually pinnately or bipinnately compound, with deeply pinnately lobed leaflets. The large leaves are covered in scales and hairs, and bear sori (spore clusters) on their undersides. The sori are often covered by a flap of tissue called an indusium, a useful characteristic for classifying the Cyatheaceae. Some indusia are cup-shaped (cyatheoid), while others are hood-shaped (hemitelioid), enclose the sorus (sphaeropteroid), or scaly. Like most ferns, members of the Cyatheaceae are homosporous. Cyatheaceae are found in both New and Old World tropical wet montane forests and cloud forests, with some species extending into south-temperate regions. Most Cyatheaceae are terrestrial, with one sometimes being epiphytic and others having a creeping habit, but these are exceptions to the family norm.
Cyatheaceae can be distinguished from arborescent Dicksonia by the presence of scales, the position of the sori, and the morphology of sporangia and spores. In the Cyatheaceae, the sori occur away from the margins of the pinnules, and are elongate or rounded.
Since the exact number of species is not known, classification of the Cyatheaceae has had a long and controversial history, and is still undergoing revision. Three tentative 'clades' have been developed: Alsophila, Cyathea, and Sphaeropteris. These are frequently used as genus names. Cnemidaria, Trichopteris (or Trichipteris), and Nephelea (or Nephelia) have also been suggested as genera. Initially, indusium and scale morphology were used to organize the Cyatheaceae into taxonomic ranks. Most recently, plastid DNA has been used, suggesting the Cyatheaceae should be split into four clades: Sphaeropteris, Cyathea, Alsophila, and Gymnosphaera + A. capensis. However, it remains unclear which of these groups should be considered genera and which are subgenera. These groupings will undoubtedly change as the molecular phylogeny of the Cyatheaceae is refined.
- Korall, P., K.M. Pryer, J.S. Metzgar, H. Schneider, and D.S. Conant. 2006. Tree ferns: monophyletic groups and their relationships as revealed by four protein-coding plastid loci. Molecular Phylogenetics and Evolution 39: 830-845.
- Judd, W.S., C.S. Campbell, E.A. Kellogg, P.F. Stevens, and M.J. Donoghue (Eds.) 2008. Plant Systematics: A Phylogenetic Approach, Third Edition. Sinauer Associates, Sunderland, Massachusetts, USA.
- Korall, P., D.S. Conant, J.S. Metzgar, H. Schneider, and K.M. Pryer. 2007. A molecular phylogeny of scaly tree ferns (Cyatheaceae). American Journal of Botany 94(5): 873-886.
- Holttum, R.E. and P.J. Edwards. 1983. The tree-ferns of Mount Roraima and neighbouring areas of the Guayana highlands with comments on the family Cyatheaceae. Kew Bulletin 38(2): 155-188.
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