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Psilotum nudum, the whisk fern, [3] is a fernlike plant. Like the other species in the order Psilotales, it lacks roots. [4]Its name, Psilotum nudum, means "bare naked" in Latin, because it lacks (or seems to lack) most of the organs of typical vascular plants, as a result of evolutionary reduction.
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.
Psilotaceae is a family of ferns (class Polypodiopsida) consisting of two genera, Psilotum and Tmesipteris with about a dozen species. [1] It is the only family in the order Psilotales . [ 2 ]
There are four extant eusporangiate fern families, distributed among three classes. Each family is assigned to its own order. [1] [2] Class Psilotopsida. Order Psilotales, family Psilotaceae – Whisk ferns (2 genera, about 17 species) Order Ophioglossales, family Ophioglossaceae – Adder's-tongues (5 genera, about 80 species) Class Equisetopsida
Below are lists of extant fern families and subfamilies using the classification scheme proposed by the Pteridophyte Phylogeny Group in 2016 (PPG I). [1] The scheme is based on molecular phylogenetic studies, and also draws on earlier classifications, [1] particularly those by Smith et al. (2006), [2] Chase and Reveal (2009), [3] and Christenhusz et al. (2011). [4]
They placed the whisk ferns and related taxa in the class Psilotopsida, with two orders. [2] Mark W. Chase and James L. Reveal (2009) classified them as two separate subclasses, Psilotidae and Ophioglossidae, corresponding to those orders within a much broader grouping, the class Equisetopsida sensu lato . [ 3 ]
Some botanists believe P. complanatum is a survivor from a very primitive lineage of fern-like vascular plants. [3] Psilotum complanatum lives in moist evergreen forests on the Malay Peninsula, Australia, Fiji islands, Mexico, Hawaii and South America. In India it is reported only from the Nicobar group of islands.
Living order of Lycophytes and ferns are taken from Christenhusz et al. 2011b [2] and Pteridophyte Phylogeny Group. [3] Living orders of Gymnosperms are added from Christenhusz et al. 2011a [4] while extinct orders are from Anderson, Anderson & Cleal 2007. [5]
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