On what basis are such plants as parasites rafflesia, broomrape, Peter’s cross considered plants?

Let’s take a look at the example of rafflesia. They cannot photosynthesize. But still, rafflesia, like other predatory plants, belongs to plants. The fact is that these organisms lead a fixed lifestyle. They have flowers as well as fruits. This is not typical of other organisms that lead a fixed lifestyle – fungi, which are also heterotrophs. Representatives of other kingdoms also have such ambiguous properties. For example – sea slug, which belongs to animals, is able to photosynthesize.