Marattiopsida
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 Mule's-foot fern (Angiopteris evecta)
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Class Marattiopsida is a group of ferns containing a single order, Marattiales, and family, Marattiaceae. Class Marattiopsida diverged from other ferns very early in their evolutionary history and are quite different from many plants familiar to people in temperate zones. Many of them have massive, fleshy rootstocks and the largest known fronds of any fern. The Marattiaceae is one of two eusporangiate fern families, meaning that the sporangium is formed from a group of cells vs the leptosporangium in which there is a single initial cell. There are four extant genera (Angiopteris, Christensenia, Danaea and Marattia) and it has a long fossil history with many extinct taxa (Psaronius, Asterotheca, Scolecopteris, Eoangiopteris, Qasimia, Marantoidea, Danaeites, Marattiopsis, etc.)
In this group, such fronds are found in the genus Angiopteris, native to Australasia, Madagascar and Oceania. These fronds may be up to 9 meters long in the species Angiopteris teysmanniana of Java. In Jamaica the species Angiopteris evecta is widely naturalized and is registered as an invasive species. The plant was introduced by Captain Bligh from Tahiti as a staple food for slaves and cultivated in the Castleton Gardens in 1860. From there it was able to distribute itself throughout the eastern half of the island.
Another East-Asian genus is Christensenia, a peculiar fern with fronds resembling a horse chestnut leaf. That is why the species is called Christensenia aesculifolia, meaning Christensen's chestnut-leaf. Christensen was a famous Danish fern botanist.
The most widespread genus in Marattiaceae is the pan-tropical Marattia, usually ocurring at higher elevations. These are also large ferns with globular rhizomes, but fronds can be up to 4 times pinnate. The sporangia are fused into bivalvate structures called a synangium. The New Zealand King Fern, Marattia salicina, known in Maori as Para also belongs here. Sometimes called the Potatoe Fern, this is a large Australasian fern with an edible fleshy rhizome that is used as a food source by some indigenous peoples.
The forth genus Danaea is endemic to the Neotropics. They have bipinnate leaves with opposite pinnae, which are dimorphic, the fertile leaves much contracted, and covered below with sunken synangia.
Several other genera are known in the Marattiaceae, namely: Archangiopteris, Macroglossum, Protangiopteris, and Protomarattia. These are all synonyms of Angiopteris.
According to recent molecular studies it appears that these eusporangiate ferns are a sister group to the horsetails (Equisetaceae).
See botanyphotos.net [1] for many images of Marattiaceae.
