Complex sentence: Some varieties are able to parasitise a single plant species, eg "Orobanche hederae", Ivy broomrape, is restricted to "Hedera helix" while others can infect a whole family such as "O. minor" on Trifoliata and possibly other Papilionaceae.
Split into simpler sentences: Some varieties are able to parasitise a single plant species, e.g. Ivy broomrape, "Orobanche hederae", is restricted to parasitising "Hedera helix". Others can infect a whole family, such as "O. minor" on "Trifoliata" and possibly other Papilionaceae.