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Psilophyte
Psilophytopsida is a now obsolete Class (biology), class containing one Order (biology), order, Psilophytales, which was previously used to classify a number of extinct plants which are now placed elsewhere. The class was established in 1917, under the name Psilophyta, with only three genera (''Rhynia'', ''Horneophyton'' and ''Psilophyton'') for a group of fossil plants from the Upper Silurian and Devonian periods which lack true roots and leaf, leaves, but have a Vascular tissue, vascular system within a branching cylindrical stem. The living Whisk fern, Psilotaceae, the whisk-ferns, were sometimes added to the class, which was then usually called Psilopsida. This classification is no longer in use. The class should not be confused with the current use of the name Psilotopsida, which refers to a class of living ferns, containing only Psilotaceae (whisk-ferns) and Ophioglossaceae (moon-worts and adder's-tongue ferns). Description The class was created in 1917 by Kidston and Lan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Whisk Fern
''Psilotum'' is a genus of fern-like vascular plants. It is one of two genera in the family Psilotaceae commonly known as whisk ferns, the other being ''Tmesipteris''. Plants in these two genera were once thought to be descended from the earliest surviving vascular plants, but more recent phylogenies place them as basal ferns, as a sister group to Ophioglossales. They lack true roots and leaves are very reduced, the stems being the organs containing photosynthetic and conducting tissue. There are only two species in ''Psilotum'' and a hybrid between the two. They differ from those in ''Tmesipteris'' in having stems with many branches and a synangium with three lobes rather than two. Description and life cycle Whisk ferns in the genus ''Psilotum'' lack true roots but are anchored by creeping rhizomes. The stems have many branches with paired enations, which look like small leaves but have no vascular tissue. Above these enations there are synangia formed by the fusion of three ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |