Tree wormwood (Artemisia arborescens) is a common plant along the shores of the Mediterranean; it was probably brought from Europe to the eastern Mediterranean region by man. The present paper characterizes the composition and chemical variety of the essential oil of a wild population in Israel and compares them with those of plants in a genetic collection in our possession, which originated in cultured or wild populations abroad. This examination may offer clues as to the affinity and origins of the tree wormwood of Israel. Moreover, the exploration of this issue may assist historical research into the routes followed by the crusaders. Tens of compounds were identified in the essential oil of individual plants collected from a population at the Montfort Fortress site. These compounds included -thujone, -thujone, camphor and chamazulene. There were wide variations among individual plants, and three main chemotypes were identified according to the levels of their main compounds, camphor and thujone: a "camphor" type (52% of the individuals); a "-thujone" type (14% of the individuals); and a type containing both compounds (34%). The results suggest that the origins of the plants in Israel may be characterized by comparing them with plants from natural populations abroad. It follows that the tree wormwood of Israel may not all originate from the same place. In herbarium samples collected or received from abroad, those originating in Italy included fewer individuals of the camphor type. This finding is also consistent with the hypothesis that the tree wormwood of the Montfort site originated in Europe.