FRUCTIFICATIONS FROM THE MAZON CREEK FLORA 



Text fig, 



4 - Fertile pinna of Stellatheca 

 ornata. 



gutbieri . In the Mazon Creek flora 

 this similarity is not obvious, because 

 sporangia of Oligocarpia are often 

 filled with rock matrix. From the mono- 

 graph on Oligocarpia by Abbott (1954) 

 it becomes clear, however, that there 

 are several similarities. Although the 

 form, shape, and position of the sori 

 are similar (fig. 7-10 of Abbott, 1954) 

 in both genera, the sori appear to be 

 slightly more regularly arranged in 

 Stellatheca . Stellatheca has 6 to 15 

 sporangia per sorus, while Oligocarpia 

 has 4 to 17, with 4 or 5 sporangia 

 being the most common number. One 

 to three sporangia occur in the center 

 of larger sori of Oligocarpia and in all 

 sori of Stellatheca . While there is a possibility of overlap of Stellatheca and 

 Oligocarpia based on some soral characters, there is a distinct difference be- 

 tween the variable appearance of the pinnules of Oligocarpia and the regular out- 

 line of the pinnules of Stellatheca. The main difference between the genera is 

 the apparent dissimilarity of the sporangial wall. The annulus of Oligocarpia 

 is much more clearly defined than anything which could be called an annulus in 

 Stellatheca . 



The sporangia of S. latiloba were considered exannulate by Danze (1956). 

 The wall pattern consists of rows of elongate cells and an apical plate of isodia- 

 metric cells. This description resembles that of sporangia of Discopteris Stur, 

 1883: some authors interpreted them as exannulate, and others regarded the apical 

 plate as an annulus. A reinvestigation of type specimens of Discopteris revealed 

 that the lateral cell walls constituted a massive annulus and that there was an 

 apical plate (H. W. Pfefferkorn, in press). A longitudinal groove observed in 

 sporangia of Stellatheca in Mazon Creek specimens is interpreted as a region of 

 dehiscence. As in Discopteris there is a two-ridged appearance on the largest 

 pinna axis (n-3), which may indicate an H- or U-shaped vascular strand. 



The spores in Oligocarpia are minutely punctate, and in Stellatheca spores 

 show a strong ornamentation. The ornamentation is probably a real difference al- 

 though the spore size range is quite similar (29 to 38 \±m in Oligocarpia and 19 to 

 37 [im in Stellatheca) . 



Stellatheca and Tedelea (Eggert and Taylor, 1966) possess several simi- 

 larities. The marginal position of the sori is the same. In Tedelea the lateral 

 veins fork only once and each branch bears one sorus. In Stellatheca a similar 

 arrangement can occur in very small or young pinnules but normally a lateral vein 

 is forked twice and gives rise to three sori. The differences between the two 

 genera are, however, more numerous. While Tedelea has occasionally solitary 

 sporangia and usually 2 to 7 sporangia per sorus, Stellatheca has 6 to 15. The 

 sori, as well as the sporangia within a sorus, of Stellatheca have a much more 

 regularly arranged appearance. The spores are entirely different in their orna- 

 mentation. The foliage in the two genera is somewhat but not very different, 

 judging from the reconstruction of Eggert and Taylor (1966). 



In the specimens described from Mazon Creek there is some superficial 

 similarity between Stellatheca and Asterotheca in the kind of preservation. Astero- 

 theca , however, has no central sporangia in a sorus and has smaller pinnae, smal- 

 ler pinnules, and fewer sporangia in a sorus. 



