Yes, that page is currently unavailable. Maybe it's being updated.
I'm well aware of the definition of taxonomic synonyms, which are obsolete genus or species names that have been reclassified as a different genus or species. This is the definition the Catalogue of Life uses, and it's the definition we use in our database.
The Plant List (which I rarely consult because it's woefully outdated) also names Zinnia hybrida as a synonym of Z. peruviana and the common (horticultural) use 0f Zinnia hybrida as an unresolved name.
http://www.theplantlist.org/tp...
http://www.theplantlist.org/tp...
ITIS is a reliable source, though not as up to date as the Catalogue of Life, but it is limited and doesn't include Zinnia hybrida among its entries.
