>Bill and Ian,
>Do you think that the tridentata ancestor may have been shoved down
>the middle of the continent by the last glacier and had to evolve
>more to adapt to the climate that developed in the south? Did the
>glacier(s) come down that far?
The last glacial maximum angled down into northern PA, across central OH,
IN and IL, then cut NW. There was evidently a large unglaciated area in
central Wisconsin (called the Driftless Area). Your idea may be right.
But today tridentata occurs mostly in the south Atlantic coastal plain.
I still think it legitimate to question its relationship to setosa/hookeri.
Department of Biology
Hampden-Sydney VA 23943