Ondontopteris genuina in Rhode Island

Eda M. Round
1921 Botanical Gazette  
One of the most characteristic and common fossils of Rhode Island is Odontopteris genuina Grand'Eury. These plants apparently grew to great size around the coal swamps of the Narragansett Basin during the Carboniferous, somewhat like the tree ferns of the tropical forests of the present day (fig. I). The fronds appear to have been bifurcate, the angle formed by the branches being about go9 (fig. 2). The rachis is striated and clothed with short pinnae, the latter having enlarged pinnules at
more » ... ged pinnules at their tips and being more separated than those of the expanded parts of the frond. The pinnae vary considerably, sometimes being short or at other times attaining a length of over I5 cm. The pinnules often vary in shape on the same specimen, some being falcate and acute, while others are oval and rounded at their apices. The acute type of 0. genuina is very common in the state, and may have come about as a result of the conditions under which the fossils were originally imbedded. The pinnules appear to have been firm in texture and convex or "bombe" in shape. If these shapes were squarely imbedded they would appear oval ( fig. 3a) when fossilized, while more pointed effects would result from preservation at a slight angle ( fig. 3b; fig. 4a, b) , and long, narrow effects from still greater angles (fig. 5a ). While these forms have pinnules 3-8 mm. broad by io-I6 mm. long, the illustrations from Pawtucket show much larger sizes and resemble those figured by ZEILLER' from Commentry, France. The Pawtucket specimens do not appear to have been as firm and thick as the smaller Rhode Island types, and the borders are inclined to be less even. The pinnules also were evidently flat rather than convex in shape and somewhat cyclopterid in appearance ( fig. 3c, d; fig. sb ).
doi:10.1086/332945 fatcat:px6zb3enljadvjsypj2ay6us4u