I do not agree it's a synonym. All European websites (unfortunately none of them in English) tell me that there is a difference. The flowers of the T. erecta (African marigold) are bigger and higher than the flowers of the T. patula (French marigold)
And here is a link to a scientific article about the T. patula and T. erecta. They speak also of different species. .
http://jxb.oxfordjournals.org/...
