Are cactus phylloclade and sweet potato homologous?

Cactus phylloclade and sweet potato are both modified stems that store water and nutrients, but they are not homologous structures. Homologous structures are those that have a similar evolutionary origin and developmental pathway, while analogous structures are those that have a similar function but do not share a common evolutionary origin or developmental pathway. In this case, the cactus phylloclade is a modified stem that has taken on the function of a leaf, while the sweet potato is a modified stem that has taken on the function of a root. Therefore, they are analogous structures.