Complex sentence: In the wild, the species is seriously threatened by a root disease, caused by the introduced fungal pathogen "Phytophthora lateralis"; this disease is also a problem for horticultural plantings in some parts of North America.
Split into simpler sentences: In the wild, the species is seriously threatened by a root disease caused by the introduced fungal pathogen, "Phytophthora lateralis". This disease is also a problem for horticultural plantings in some parts of North America.