I found this book available as a free download at:
While it appears to be only for bee keepers, it’s advice can also be applied to butterflies and all pollinators.
It’s a bit daunting when first look at the 312 pages, but becomes easier to use if you do a search for your specific state.
I’ve found that many of the plants and trees I have planted are listed in this book.
Did you know that TULIP-POPLAR or TULIP TREE (Liriodendron tulipifera) is a good nectar plant?