Heather, welcome it IS important to call things by their right name and you guys writing those labels complete with cultural instructions, what a responsibility. I think William Stearn is the recognized authority on botanical Latin and he did compile a dictionary. The RHS 'Plant Finder' seems to be cutting edge and have been calling buddleia buddleja for years but still insists that lupine is lupin. As long as you are consistent, consistently accurate that is, and blame it on your source I guess you are covered.

The basic information in Hortus III is sound, but it doesn't reflect currently used nomenclature. It also doesn't include the vast numbers of plants that have been introduced in the nearly 30 years since its publication. I check nomenclature for one garden book publisher and write for another, and they both use the American Horticultural Society A-Z Encyclopedia of Garden Plants as their primary reference. The previous edition was in 1997; the more recent one was released last October. While it has some flaws (such as some questionable hardiness zone ratings), it is quite comprehensive and about as current as you can get. Good luck!

For what it's worth, Dave's Garden still considers Hortus to be the authority when it comes to botanical Latin names.

With names changing on what appears to be a far too regular basis, and heat zones now being increasingly recognized, the online sources seem to be the most up to date.