II. ASPIDIE.1^1 



Fronds not articulate to the rhizome; sori terminal or dorsal on their 

 veins, usually rovmd, exceptionally extending along the veins or over 

 the parenchyma; indusia fixed by the center or at the top of a basal 

 sinus, never elongate, frequently wanting. 



Because the pi-esence or absence of the indusium varies within the 

 larger genera, and even in some of their species, no classification and 

 arrangement of the Aspidiece is everywhere easy to use. But, for this 

 reason, any arrangement which tries to define its genera primarily by 

 this character is eminently artificial and impractical. 



This is the largest group in our fern flora, and, except for the genera 

 whose sporangia cover the dorsal surface, it is a very natural one, 

 distinguished from the Polypodiece by the nonarticulate stipe and the 

 usually present indusium, from Aspleniew by the round sorus and indusium, 

 and from Davalliea; by the latter's mode of attachment. 



1. Frond pinnate or pinnately veined. 



2. Sori definite, confined to ttie veins, fertile frouds or 

 segments not siiarply differentiated. 

 3. Veins free. 



4. Indusium oval, attached by its axis (2) DidymocMcena 



4. Indusium orbicular, attached by its center.. (3) Poh/stichum 



4. Indusium cordate-reniform or wanting (4) Lastraea 



3. Lowest veinlets of neighboring veins uniting to 

 form regular triangular areolae, usually with 

 a series of regular areolae outside. 



4. Sori round (4) Ncphrodium 



4. Sori elongate along the cross-veinlets (5) Mcnisciiun 



3. Veins anastomosing copiously (6) Aspidium 



2. Fronds or their segments dimorphous, sori covering 

 the parenchyma. 



3. Veins free (.7) Polyboh-ya 



3. Veins anastomosing. 



4. Veins free toward the margin (8) Stenosemia 



4. Veins anastomosing throughout (9) Gymnopteris 



1. Frond and venation dichotomous ilO) Diptcris 



(2) DIDYMOCHLAENA Desvaux. 



Fronds at least bipinnate, the basiscopic half of the ultimate divisions 

 almost suppressed; veins free, branched; .sori terminal on them but not 

 marginal, somewhat elongate; indusium the shape of the sorus, fixed along 

 the middle, opening on all sides. A single variable species, terrestrial 

 in most tropical countries, resembling a lAndsaya more than any of its 

 relatives in Aspidietr. 



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