The term “synonymous” was formerly associated with auxin, specifically referring to indole-3-acetic acid (IAA), which is no longer utilized. The initial assertions of naturally occurring auxins, designated as a and b, were believed to be cyclopentene acids and contributed to the recognition of IAA as the “distinct” auxin. However, to date, these purported cyclopentene acids have not been successfully extracted, and there are reservations regarding their actual existence.