196 



genus aspidium. The different generic divisions here adopted are based 

 on the form of the sori and involucres in conjunction,* partty, with 

 venation and habit. In Aspidium proper these organs are generally 

 completely circular in the three following genera they are orbicular-re- 

 niform, of which Nephr odium embraces the great majority of species ; 

 while in the last, a monotypic genus, the sori are much larger, and 

 double like a horse shoe, with a very deep sinus. The majority of the 

 hardy and coarse obtrusive, wayside ferns belong to this tribe, though 

 as many are equally seclusive and retreat-loving. The distribution is 

 universal in tropical and temperate regions, entering both the arctic and 

 antarctic zones. 



Sori circular, involucres pellate-orbicular, free round the entire 

 edge. — A sp id ium. 



Sori circular or punctiform, involucres cordate-orbicular, attached by 

 the sinus. — Nephrodium. 



Sori and involucres reniform, the latter attached by the sinus, 

 terminal on the veins. — Nephrolepis. 



Sori and involucres reniform, the latter attached by the sinus, 

 oblique with the veins, near the base or distant from the margin. — 

 Oleandra. 



Sori and involucres large, folded, with a deep sinus, the shape of a 

 horse shoe. — Fadyenia. 



Genus XXI Aspidium, Swartz. 



Sori orbicular, rarely orbicular-renif orm ; receptacles dorsal, medial, 

 compital, or terminal on the veins ; involucres superior, the same shape, 

 centrally or eccentrally attached, deciduous or persistent at maturity ; 

 venation free, branches anastomosing, or copiously areolated ; fronds 

 widely variable in form, texture and size. 



This genus forms the smaller of the two principal generic divisions 

 of the tribe ; it numbers over a hundred species which range round the 

 world in the tropical and temperate zones, two or three extending to 

 the arctic and antarctic regions. The majority are of hardy accommo- 

 dating constitution, and frequent open and half shaded situations with 

 equal success and freedom. In the greatly preponderating and typical 

 form of the sori, the involucres are quite free around the circular edges, 

 and are eventually shrivelled up in the centre of the sorus or are quite 

 dislodged by the matured sporangia, in which latter case the plants 

 resemble and might be mistaken, as they often have been, for true 

 Polypodia. In some species however, there is a manifest tendency in 

 the form of the sori and involucres to the reniform condition which 

 characterises true Nephrodia. 



a. Veins free. 



b. Fronds entire or 1 — pinnate. 



Fronds entire, or with the base only lobed. 1. A. Plaschnickainum. 

 Fronds entire at the top, the base bipinuate. 2. A. rhizophyllum. 

 - Fronds pinnatifid or pinnate, the pinnae adnate at the base. 3. A. 

 glandulosum. 



Fronds pinnate, pinnae quite entire. 4. A. semicordatum. 



Fronds pinnate rachis densely paleaceous. 5. A mucronatum. 

 b. b. Fronds pinnate or bipinnate. 6. A. triangulum. 7. A. tridens. 

 8. A. viviparum. 



