6 Polypodiaceae 



Tribe 2. Aspidieae. Sori circular or subcircular in 

 outline, flattish ; indiisium attached centrally, peltate. 



Sorus cordate, indusium reniform, attached in the 

 sinus or absent. Dryopteris (including Phegopteris). 



Sorus circular, indusium attached in the centre. 



Polystichum. 



Tribe 3. Asplenieae. Sori elongated to linear, de- 

 veloped along veins from which the lateral indtisium 

 springs. 



Subtribe i. Blechiiinae. Sori on veins parallel to 

 the midrib of pinna or pinnule of special fertile leaves. 



Only British genus : Blechnum. 



Subtribe 2. Aspleninae. Sori on lateral veins of 

 pinna or pinnules of ordinary fronds. 



Indusium with single flap entire. Asplenium. 



Indusium with single flap, margin lacerate. 



Athyrium. 



Indusium with two flaps, one on either side of sorus. 



Scolopendrium. 



Tribe 4. Pterideae. Sori elongated to linear, de- 

 veloped along special veins. Indusiuju mostly absent, 

 sometimes developed as an infolding of the leaf margin. 



Subtribe I. Gymnograinminae. 5^n" occupying the 

 whole of the fertile veins. 



Only British genus : Gymnogramme. 



Subtribe 2. Cheilanthinae, Sori occupying the 

 distal ends of the fertile veins. 



Only British genus : Cryptogramme. 



Subtribe 3. Adiantinae. Sori occupying the distal 

 ends of the fertile veins, within the revolute leaf margin. 



Only genus : Adiantum. 



