This name is a synonym of Robinia pseudoacacia f. monophylla-pendula (Dieck) Voss.
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 100349817) with original publication details: Ill. Gehölzb. ed. 2: 332 1892.
This name was in version 1 of The Plant List, record tro-100349817.