I checked on the Kew records and found this entry
Alocasia plumbea Van Houtte, Fl. Serres Jard. Paris, II, 11: 93 (1875). This name is a synonym of Alocasia macrorrhizos (L.) G.Don in R.Sweet, Hort. Brit., ed. 3: 631 (1839).
Also, the IAS doesn't have an entry for A. plumbea on its list. Haven't seen any discussions on the issue.