This is not about Canadian gardening -- I have just been reading about the Indonesian Rafflesia. It is referred to as a flowering plant, but terms such as "infects the host", "no roots" and "lives inside the host" make it sound much more like a fungus. Given that it has no roots, what does it use to remain attached to the host?
It's not known how it gets started on the host vine but afterward - yes - the whole thing except the flowers lives inside the host stems. Maybe as with mistletoe the seeds stick to the bark of the host and then penetrate as though growing into soil, in the manner of non-parasitic plants.
Of interest: 'World's biggest flower' that smells like ROTTING FLESH blooms in Indonesia | Daily Mail Online Rafflesia tuan-mudae - Wikipedia
The spaces between the cell walls of plants are filled with pectin, much like cartilage prevents our bones from rubbing against each other. This is one space a parasite can grow within, or it can penetrate into the symplast, which is the interconnected living parts of plant cells. As an aside, there are plenty of organisms that live within plants (and us): Endophyte - Wikipedia