Technical Abstract: Hypericum androsaemum is a valuable landscape plant that is potentially invasive in certain parts of the U.S. Infertile, non-invasive, cultivars of H. androsaemum with desirable ornamental features would be ecologically beneficial and valuable for the horticultural industry. Male and female fertility of ten triploid H. androsaemum, developed with a combination of variegations and foliage colors, was investigated under greenhouse (controlled pollinations) and field conditions (natural pollination). Male fertility was evaluated based on pollen viability tests (pollen staining and pollen germination). Female fertility was based on fruit set, seed set, germination capacity of seeds, and number of seedlings produced for each flower. Values for different measures of fertility varied among triploid clones; pollen germination was significantly reduced for all triploids and nine of the ten triploids produced no viable seed representing 100% failure of approximately 171,000 potential fertilization events (based on fertility levels of diploid controls). The remaining triploid clone produced 2 seedlings per flower (compared with 260 for the controls), but those seedlings died shortly after germination. This research documented that these triploid H. androsaemum are highly infertile with no measurable female fertility. These clones will provide ideal alternatives to fertile forms of H. androsaemum where naturalization is a concern. These methods also provide a rigorous protocol for evaluating fertility of other taxa that are selected or developed as non-invasive cultivars of potentially weedy species.