A periphery, (Fr: couronne) is an INSEE (French demographic statistics institution) statistical area[1] designating a commuter belt around an urban unit (Fr: unité urbaine). Together these complete the INSEE urban area statistical area.
Based on France's commune system (interlocking administrative subdivisions often comparable to civil parishes, towns or cities), a commune is considered part of a couronne when
- it is not densely constructed enough or is too isolated to be part of any unité urbaine (or "pôle urbain" if it is the core of the agglomeration), and
- at least 40% of its population commutes to workplaces in a unité urbaine or pôle urbain, or to another commune connected to a unité urbaine through the same criteria.
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Well, that’s interesting to know that Psilotum nudum are known as whisk ferns. Psilotum nudum is the commoner species of the two. While the P. flaccidum is a rare species and is found in the tropical islands. Both the species are usually epiphytic in habit and grow upon tree ferns. These species may also be terrestrial and grow in humus or in the crevices of the rocks.
View the detailed Guide of Psilotum nudum: Detailed Study Of Psilotum Nudum (Whisk Fern), Classification, Anatomy, Reproduction