EARLY PENNSYLVANIA FLORA FROM WEST-CENTRAL ILLINOIS 21 



(or leaves ?) are broadly attached and are not spread out in the plane 

 of the frond. They resemble the fertile leaves of the noeggerathialean 

 cones in their three-dimensional arrangement. 



PTERIDOSPERMS 

 Genus: Megalopteris (Dawson) Andrews 



Synonymy 



1828 Cannophyllites, Brongniart, Prodr., p. 130 



(nomen rejiciendum; see Stafleu et al., 1972, 

 p. 376) 



I865 Neuropteris, Hartt in : Bailey, p. 550 



1871 Neuropteris {Megalopteris) Dawson, p. 51 



1875 Megalopteris (Dawson) Andrews (nomen conservandum; 

 see Stafleu et al. , 1972, p. 376) p. ^15 



Description . — Simple pinnate leaf, pinnules often attached at 

 irregular distances and at irregular angles, giving the impression of a 

 pedate frond near the top; pinnules strap-like or lanceolate, generally 

 large; strongly decurrent base of pinnule with unequal sides; midvein 

 thick, longitudinal striations often present; lateral veins dense and 

 forking one to three times, curved or straight. 



Discussion . — Megalopteris has repeatedly been compared with 

 Alethopteris, There are indeed a number of similarities, like the ve- 

 nation in some species, the decurrent base of the pinnules, and the 

 overall shape of the pinnules. However, there are distinct differences. 

 Alethopteris has pinnules that are very regular in their angle of at- 

 tachment, and the leaf shows several orders of pinnate divisions whereas 

 the leaf of Megalopteris is only simple pinnate. 



The notion that Megalopteris has a pedate leaf has been derived 

 from a specimen of Megalopteris fasciculata Lesquereux, which was fig- 

 ured by Lesquereux, 1879 (Atlas), on plate 2k , figure 2. The specimen 

 (USNM 1170^0 is reproduced photographically here on plate 6, figs. 1 

 and 2. The leaf appears to be pedate at the base, but is clearly pin- 

 nate higher up. All specimens at our disposal were pinnate. 



Pinnules vary greatly in size within one leaf. This variation 

 is expressed in nearly every characteristic of the pinnules. In several 

 species the angle of lateral veins, for instance, changes within one 

 pinnule. It is thus quite difficult to find any consistent characteris- 

 tics that are useful in the delineation of species. There are 15 species 

 of Megalopteris mentioned in the literature, but only six seem to be 

 distinguishable on the basis of reasonably objective characteristics. 

 Only two species, Megalopteris dawsoni and M. ovata 9 occur in the Spen- 

 cer Farm Flora. 



