Hallo Susan,
is this your gr-grandfather Carl Bernhart Heinrich Stier (1865-1928) – Find a Grave Gedenkstätte. There is no Planeu in Saxony but i could be Pausa because his wife came from Mühltroff a place near to Pausa. Here you can read something about that places in Saxony Mühltroff – Wikipedia. For more informations you should take the list for Sachsen (Saxony).
I work since many years on emigrants from Oldenburg and in some cases I found Benhart for Bernhard. I think it came from an combination between "Ben" and "Bernhard" because "Bernhard" was to difficult for English speaking people. Roman-Catholic persons mostly took the Latin form Bernard. That was easier in the USA.
Best regards,
Gunter