Consistent and inconsistent classification of genes. i) A subtree of a gene tree classified consistently. The stem symbol here is "xxx". ii) A subtree (shown in bold) that is classified consistently, and that is part of a larger tree not classified consistently. The conflict occurs at the node marked by the zigzag symbol. iii) An example of a subtree that features two subfamilies. iv) An example of a subtree of ABC genes classified consistently. v) An example of a subtree of an ABC gene tree not classified consistently. Again, the zigzag symbol marks the conflict.