I've given up there too, I don't think they have a database on line.
I did a bit of research and found the reference for 'Purpurea' as the cultivar name. It is in Notes on Tradescantia pallida: American Commelinaceae: III
D. R. Hunt
Kew Bulletin, Vol. 31, No. 1 (1976), p. 104
"...I propose that Boom's species be treated as a cultivar , to be named Tradescantia pallida cv. ' Purpurea ' ......."
