Dear PaleoListserv member,
I am interested in changes of venation patterns in response to changes in 
environmental parameters (temperature, water availability, elevation etc.). So 
far I found that several modern species of Salix subg. Protitea (according to 
Skvortsov an evolutionary “retarded” subgenus) may vary from 
eucamptodromous to brochidodromous (semicraspedodromous?), and to 
producing straight intramarginal veins as a function of latitude. As an example, 
Salix nigra is eucamptodromous in Quebec and northeastern USA, and 
brochidodromous in Florida, Texas, and Mexico). Because of overall climate 
cooling since Eocene times one would expect to find more brochidodromous 
Salix leaves in the fossil record than in modern Salix leaves from similar 
latitudes. This does, however, not seem to be the case. Has anybody seen S. 
nigra –like fossil leaves (e.g. S. inquirenda, S. succorensis, S. desatoyana or 
any other long, narrow-leaved species) with a brochidodromous 
(semicraspedodromous?) venation or an intramarginal vein? I am attaching an 
image of a cleared S. nigra leaf (from Mexico) as an example of a 
brochidodromous (semicraspedodromous?) venation pattern. I would very 
much appreciate any feedback on this matter.
Sincerely,
Walter Buechler