Ken, I've done a bit of googling, not what you're looking for but it was an education, I never knew they were in the willow family.
Your original native black poplar and the one in historic buildings would have been populus nigra spp betulifolia I think? According to Wikipedia it is now becoming rare. The pictures I've seen are a tree of broader habit much like our native cottonwoods.
P.nigra spp lombardy, a columnar subspecies was introduced from Italy but did not tolerate the climate well.
Lombardy and betulifolia were crossed in the 1880's to yield P. nigra spp plantierensis which you mention above. I believe this is what is commonly called a lombardy poplar in England.
I've had an enjoyable round of emails with a dendrologist although this is not his area of expertise.
"Our" Lombardy is Populus nigra 'Italica' - selected for its columnar propensity and propagated from rooted cuttings. They are all genetically identical and come from a northern Italian Populus nigra parent tree. Populus nigra is the widespread European black poplar. Within Populus nigra there are several recognized subspecies, including the rare subspecies betulifolia. Populus nigra 'plantierensis' is also an upright Populus nigra clone. The parent tree was derived from a cross between an 'Italica' clone and a Populus nigra subsp betulifolia tree. I would bet that it is still called a Lombardy.
At least P. nigra 'Italica' is what I think is the most commonly planted over here (photos of 'plantierensis' show broader crowns than most of what we call Lombardy and most of our tree books only refer to 'Italica'). I wouldn't be surprised if there was rampant confusion and selling of both varieties (and others?) under the name 'Italica'.
For us a lombardy may be a somewhat different tree, although maybe not, and is to both of us an introduced species.
The cottonwoods are one populus group, the aspens are the other native populus we have, both have been used for lumber but as many have said, it would probably not be the first tree out of the woods. I doubt it was there either. Mechanically it seems to be on par with white pine. The FPL has done conversion studies with aspen and recommended a Saw-Dry-Rip program.
These are some silvics links on populus;
http://plants.usda.gov/java/profile?symbol=POPULhttp://plants.usda.gov/java/ClassificationServlet?source=profile&symbol=POPUL&display=63
