What was Jerome's defense for translating the Hebrew word קִיקָיוֹן (kikayon) in Jonah 4:6, etc. into Latin as hedera?

In the Vulgate translation of Jonah 4:6–7, 4:9–10, Jerome translated the Hebrew word קִיקָיוֹן (*kikayon*) into Latin as *hedera*, which is the equivalent of the English word "ivy ." Some, including Augustine, expressed their discontent with this particular translation of Jerome. In response, what was Jerome's personal defense for his translation of the Hebrew word קִיקָיוֹן into Latin as *hedera*?