Citrus is a messy botany.  It loves to cross with anything  and in so doing creates very complex ancestry.  C-35 rootstock is a citrange and was created for its tolerance to cold, but is also good in Phytophthora situations and creates a slightly smaller tree.  Oddly, it is deciduous, a cross between Poncirus and Citrus.  It's a trifoliate hybrid.  'Meyer' lemon is the same mess, a cross between a lemon and an orange/mandarin.  You would think these two messed up cousins might do well, but in several instances there is an incompatibility.  'Meyer' has been grown successfully on 'Macrophylla' and 'Yuma Ponderosa', both of which are also complex hybrids.