II. asimdihj:. 



Fronds not articulate to tlic rliizome; sori terminal or dorsal on tlieir 

 veins, usually round, cxceijtionally extending along the veins or over 

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

 sinus, never elongate, frequently wantimr. 



Because the presence or absence of the iinlu-ium varies witliiu the 

 larger genera, atid even in some of their species, no classitication and 

 arrangement of tlie Aspidic(r is everywhere easy to use. But, for this 

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

 this character is eminently artificial ami 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 Pohjpodie(c by the nonarticulate stipe and the 

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

 and from Davalliece by the latter's mode of attachment. 



1. Frond pinnate or pinnately veined. 



2. Sori definite, confined to the veins, fertile fronds or 

 segments not sharply differentiated. 

 3. Veins free. 



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



4. Indusium orbicular, attached b>- its center.. (3) PoU/stichum 



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



3. Lowest veinlets of neighboring veins uniting to 

 form regular triangular areolse, usually with 

 a series of regular areolce outside. 



4. Sori round (4) Ncphrodium 



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



3. Veins anastomosing copiously (6) Aspidium 



2. Fronds or their segments dimorphous, sori covering 

 the parenchyma. 



3. Veins free (7) Polybotrya 



3. Veins anastomosing. 



4. Veins free toward the margin (8) Stenosemia 



4. Veins anastomosing throughout (9) Gymnopteris 



1. Frond and venation dichotomous (10) Dipteris 



(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 Littdsaya more than any of its 

 relatives in Aspidiecr. 



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