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SporePlants213-page15 - the world It occurs almost...

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Spore-Dispersing Vascular Plants - 15 "Pterophyta" (The Ferns) The ferns are the only spore-dispersing vascular plants conspicuous in the environment today. There are five orders and about 11,000 species of ferns varying from the epiphytic filmy ferns on the leaves of tropical flowering plants to the tiny aquatic Azolla to large tree ferns with leaves reaching 15 feet in length and whose roots and stems are among the toughest “wood” known. Fern diversity is greatest in the tropics, however. With the exception of a small herbaceous fern genus, Botrychium (one of the more primitive ferns), ferns do not have secondary growth. Bracken fern Pteridium aquilinum , may be the single most widespread vascular plant in
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Unformatted text preview: the world. It occurs almost everywhere, including on the Bellevue College campus. Tree Fern Polypodium Classification of Ferns Two characteristics are used to classify the five fern orders: Type of sporangia (homosporous or heterosporous) and origin of sporangium tissue (leptosporangiate {one initial} or eusporangiate {several layers}). Most ferns are in the order, Filicales. Ophioglossales – Eusporangiate Marattiales – Eusporangiate Filicales – Homosporous and Leptosporangiate Salviniales – Heterosporous and Leptosporangiate Marsileales – Heterosporous and Leptosporangiate...
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