On a Friday evening in January, a thousand people at the annual California Native Plant Society conference in San Jose settled down to a banquet and a keynote speech delivered by an environmental historian named Jared Farmer. His chosen topic was the eucalyptus tree and its role in California’s ecology and history. The address did not go well. Eucalyptus is not a native plant but a Victorian import from Australia. In the eyes of those gathered at the San Jose DoubleTree, it qualified as “invasive,” “exotic,” “alien” — all dirty words to this crowd, who were therefore convinced that the tree was dangerously combustible, unfriendly to birds, and excessively greedy in competing for water with honest native species.