PTERIDOPHYTA 



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3. Gleicheniaceae. This small family of about 130 species includes 3 

 genera, of which Gleichenia, with all the species but two, is of greatest 

 importance (Fig. 232). It is confined to the tropics and subtropics of 

 both the Eastern and Western Hemispheres. 



Fig. 233. Dicksonia antarctica, a tree fern cultivated in the Huntington Botanical Gardens 

 at San Marino, California. 



4. Hymenophyllaceae. These are the "filmy ferns," small delicate 

 forms chiefly tropical in distribution. There are about 400 species, nearly 

 equally divided between Hymenophyllum and Trichomanes. Two species 

 of Trichomanes are found in the Eastern United States. 



5. Dicksoniaceae. To this group belong 9 genera and about 125 species 

 mainly tropical in distribution. The chief genera are Dicksonia, Cibo- 

 tium, and Dennstaedtia.^ The first two are arborescent (Fig. 233). One 

 species of Dennstaedtia is found in the Eastern United States. 



6. Cyatheaceae. This is a family of tree ferns, including 3 genera and 

 about 700 species. Here belong Cyathea, Alsophila, and Hemitelia, all 

 large genera widely distributed throughout the tropics. 



^ The position of this genus is uncertain. It is often placed in the Polypodiaceae. 



