@elizatorres: Hello! This taxon swap was originally initiated by another iNat user, and I simply processed it. Seigler & Ebinger (2005; link here: http://biodiversitylibrary.org/page/12995331) decided to pull several of the taxa originally placed in Acacia—known to be polyphyletic for a while now—out and place them in the genus Vachellia. In the aforementioned publication, they simply synonymized A. farnesiana under V. farnesiana, and, to the best of my knowledge, this is still upheld in the current classification of Fabaceae. (P.S. There are still more swaps to be made [Acacia spp. to Vachellia spp.] but I simply haven't had the time to do so yet.)