CHAPTER VII 

 PTERIDOPHYTA (CONTINUED) 



4. FlLICINAEi 



The ferns constitute the largest and most representative group of pter- 

 idophytes of the present day, numbering about 7,800 species. They are 

 widely distributed over the earth, nearly all growing in moist, shady 

 places. Although making their best display in the tropics, both in num- 

 ber of species and in luxuriance of growth, they are also well represented 

 in temperate regions. The branched or unbranched stem usually bears a 

 few large, spirally arranged leaves that are sometimes simple but are gen- 

 erally divided into leaflets. There are no strobili, the sporangia being 

 very numerous on the margin or abaxial side of the leaves, or borne in 

 special structures called sporocarps. The sporangia may be solitary but 

 more commonly are borne in groups. 



Like other vascular plants, the Filicinae possess branch, leaf, and root 

 traces that arise from the stele of the stem and pass outward through 

 the cortex. In all the Filicinae, except those with protostelic stems, the 

 departure of a leaf trace causes an interruption in the continuity of the 

 stele, forming a leaf gap (Fig. 221). Leaf gaps are present in ferns and 

 seed plants but not in the lower pteridophytes. Branch gaps are pres- 

 ent, however, in all vascular plants having siphon ostelic stems (except in 

 Equisetum) . 



The Filicinae were well represented in the Paleozoic, but did not hold as 

 dominant a place in the flora as was once thought (Fig. 258). Most of the 

 fossil fern leaves found in Carboniferous deposits belong to the Cycado- 

 filicales, an order of primitive gymnosperms. Some of the Paleozoic 

 ferns may be referred to two orders with living representatives (Marat- 

 tiales and Filicales), but most of them belong to the Coenopteridales, an 

 extinct order whose relationships to the others are not clear. Living 

 ferns belong to four orders: Ophioglossales, Marattiales, Filicales, and 

 Hydropteridales. 



1. Coenopteridales 



The Coenopteridales range from the Devonian to the Permian. They 

 are regarded as the most primitive group of Filicinae, in some respects 

 resembling the Psilophytales. These ferns were all of small or medium 

 size. The stems were erect or horizontal and always protostelic. The 



' Sometimes combined with the Spermatophyta under the name of Pteropsida. 



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