Dear Sheri,
I apologize for the delayed response.
Excellent question. Sallie answered partially correct, which is to say that Magnolia liliflora is used as xinyihua, the flower buds of that species of magnolia. However, several other species are used and officially (in the Pharmacopoeia of the PRC) only M. biondii, M. denudata, and M. sprengeri are to be used.
The flowers of M. officinalis, the species that houpo is derived from, are not used as this medicine, and are, in fact, quite different, more like our native magnolia species.
M. denudata, known colloquially as yulan 玉蘭 in Mandarin, is a fairly common cultivated tree in North America. I believe, but I’m not sure, that M. biondii is also found, but less common.
I’m actually looking for a place to purchase M. denudata trees. This tree is not only medicinal but very beautiful and one of my wife’s favorite trees. If anyone knows of a good place to but a few trees, I’d be most grateful to receive that information. 🙂
I hope this helps,
Thomas