Elizabeth is a manager at a nursery and is in charge of displaying potted trees in rows. Elizabeth has 330 citrus trees and 180 palm trees. She wants to make rows of trees so that each row has the same number of trees and each tree is in a row. If the citrus trees and the palm trees must not be mixed in the rows, what is the largest number of trees that she can have in a row? The largest number of trees that she can have in a row is nothing.