The Collaborative International Dictionary of English v.0.48:
manna gum \manna gum\ n. (Bot.), A tall tree (Eucalyptus viminalis) yielding a false manna. [WordNet 1.5]WordNet (r) 3.0 (2006):
manna gum n 1: tall tree yielding a false manna [syn: manna gum, Eucalyptus viminalis]