Walter Buechler schrieb: > 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 > > Dear Walter, Can you tell me where this willow tree was growing? Why is it trying to conserve water (intramarginal vein), if it is growing on a riverbank? If there is enough water available, evapotranspiration is advantageous as it will increase the uptake of nutrients and lead to increased growth. David K. Ferguson