Interspecific hybrids between H. macrophylla and H. angustipetala and intergenerichybrids between Dichroa febrifuga and H. macrophylla were developed, verified, and described.The morphology of the interspecific and intergeneric hybrids was intermediate to the parents.Hybridity of progeny was confirmed by simple sequence repeat (SSR) markers, flow cytometry,and morphological comparisons. Interspecific and intergeneric hybrids are male and femalefertile and selected progeny are being incorporated into a H. macrophylla breeding program.The inheritance of inflorescence type (lacecap vs. mophead), purple stem pigmentation,and remontant flowering was investigated and the number and action of genes controlling thesetraits in H. macrophylla was estimated. Inflorescence type is controlled by a single gene, withlacecap dominant to mophead. Purple stem pigmentation is controlled by a single gene, withpurple dominant to green. Remontant flowering is apparently controlled by several genes, butadditional crosses are required to clarify the inheritance of this trait.