Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
arbŏrārĭus, a, um, adj. [arbor] (a technical form of arboreus), of or pertaining to trees, tree-: falx, i. e. for pruning trees, Cato, R. R. 10, 3; 31, 4; Varr. R. R. 1, 22, 5: picus, a woodpecker, Plin. 30, 16, 53, § 47: proventus, Sol. 11 and 23.
Hence, arbŏrārĭa (sc. herba), ae, f., the blackivy, as growing on trees, App. Herb. 98.