34 



GROUP RELATIONSHIPS 



not entirely satisfactory.^- The cone 

 peduncle is not demonstrable and the 

 distal tip of the cone is missing. How- 

 ever, judging from their imprint, the 

 spores are clearly of the aphanozonate 

 type and may also be represented among 



isolated spores of Triletes f^einschi. The 

 sporophylls are either verticillate or in 

 a very low spiral. There is no character 

 w^hich conflicts with its identification as 

 Sigillariostrohiis, although important 

 characters are not represented. 



RELATION OF PALEOZOIC LYCOPOD GROUPS 



Pennsylvanian sigillarians are a much 

 more specialized group than many of 

 the contemporaneous lepidodendrids. 

 These two main groups of arboreous 

 lycopods surely had a common phyletic 

 source, and there has been a tendency 

 to confuse the two groups, particularly 

 in discussions of their fructifications. 

 Consequently some discussion of certain 

 lepidodendrid genera is pertinent here 

 in order to bring out further the reasons 

 for considering them as distinct lineages 

 through Pennsylvanian and somewhat 

 later time. 



One of the chief lepidodendrid groups 

 bearing on this discussion is Lepidostro- 

 hus, a genus identified by characteristics 

 of its cones and to a large extent ap- 

 proximately correlative with Lepidoden- 

 dron. Except for the large size attained 

 by some species, Lepidostrohiis seems to 

 have been the least specialized of the 

 arboreous Paleozoic lycopods through- 

 out the Carboniferous. Mesostrohus 

 Watson (1909) appears in the lower 

 Westphalian (Mountain 4-ft. mine, 

 Clough foot, Dulesgate = Great Coal- 

 ball horizon [?]) of England and may 

 be regarded as a segregate from the 

 main line of Lepidostrohus. No great 

 specialization is manifest and it is un- 

 likely that specimens of Mesostrohus 

 can be distinguished from Lepidostro- 

 hus, when preserved as coalified com- 

 pressions. 



i2Bode (1928) indicates that only three mega- 

 spores were borne "naked" on each sporophyll of 

 S. gotJiani. The diflBculty in distinguishing' con- 

 tents of individual sporangia in compression ma- 

 terial makes the uniform presence of three mega- 

 spores doubtful. It is perhaps significant, how- 

 ever, that they were at least no more numerous 

 than in species of Mazocarpon. Bode's suggestion 

 that the spores "lie naked on the bract" and that 

 the sporangium is lacking, is too highly anomalous 

 to be accepted at its face value. He cites Flem- 

 ingitcs Carruthers (1865) as a parallel example, 

 but it was shown long ago by Binney (1871) and 

 others that Carruthers' genus was based on a 

 misconception. 



There also are some highly specialized 

 forms frequently placed with the lepido- 

 dendrids that are distinguished as the 

 Lepidocarpaceae. Whether these spe- 

 cialized forms actually belong in the 

 lepidodendrid groups (typical repre- 

 sentatives of which are Lepidodendron 

 and Lepidostrohus) or should be con- 

 sidered a separate group on a par with 

 the lepidodendrids and sigillarians, need 

 not be given special consideration now; 

 it has been discussed elsewhere (Schopf, 

 1941) and the author is inclined to think 

 segregation will prove desirable. There 

 is little reason to doubt that the 

 lepidocarps (typically represented by 

 Lepidocarpon, Illiniocarpon, and pos- 

 sibly (?) Lepidophloios) are more 

 closely related to the lepidodendrids 

 than they are to the sigillarians or any 

 other major lycopod group. ^^ However, 

 the specialization observed in Lepido- 

 carpon has been confused with the dis- 

 tinct type of specialization encountered 

 in Mazocarpon. Consequently it is 

 worth while to point out these distinc- 

 tions in somewhat greater detail. 



The Free-Sporing Character of 

 Mazocarpon 



One source of confusion arises appar- 

 ently from a misunderstanding of the 

 true morphologic nature of the Mazo- 

 carpon sporangium. Miss Benson and 

 others since 1918 have frequently termed 

 the Mazocarpon female fructifications 

 "seed-like". This terminology appears 

 unacceptable according to the writer's 

 interpretation of Mazocarpon oedipter- 

 num. The prolonged association of spor- 

 ophytic tissue with Mazocarpon mesa- 



I'^The grouping of the lepidocarps with Miadea- 

 mia under the name "Lepidospermae'' (Hirmer 

 1927) and assignment to ordinal rank by Zimmer- 

 mann (1930) seems unwarranted. Miadesmia has 

 only the remotest possible relationship with any 

 of the arboreous forms. 



