Large St. John’s wort, millepertuis majeur Large St. John’s wort, millepertuis majeur

Hypericum canadense Linnaeus var. majus A. Gray, Manual ed. 5, 86. 1867 (as major); H. mutilum Linnaeus var. longifolium R. Keller; Sarothra major (A. Gray) Y. Kimura lanceolate to narrowly elliptic, equal, 3.5–6.5 × 0.8–1.5 mm, <margins sometimes ciliate, not setulose-ciliate>, apex acute; petals golden yellow, <sometimes red-veined>, oblanceolate, 3.5–6 mm; stamens 12–21, obscurely 5-fascicled; styles 0.6–1 mm; stigmas broadly capitate. Capsules narrowly conic-ellipsoid, 4–8 × 2.5–3.5 mm, <broadest proximal to middle>. Seeds 0.5–0.7 mm; testa finely linear-scalariform. 2n = 16.

Flowering summer (Jun–Sep). Fens, marshes, ditches, lake and stream margins, other damp habitats; 0–1200 m; Alta., B.C., Man., N.B., N.S., Ont., P.E.I., Que., Sask.; Colo., Conn., Idaho, Ill., Ind., Iowa, Kans., Maine, Mass., Mich., Minn., Mo., Mont., Nebr., N.H., N.J., N.Y., N.Dak., Ohio, Oreg., Pa., R.I., S.Dak., Vt., Wash., Wis.; introduced in Europe (France, Germany), e Asia (Japan).

Hypericum majus was the western member of a vicariant species pair, differing from the originally eastern member (H. canadense) by the broader leaves, usually more-congested inflorescence, and larger flowers. These species became sympatric in glaciated northeastern North America and now hybridize freely, notably in Wisconsin (F. H. Utech and H. H. Iltis 1970). Hybrids are intermediate in form between the parents and have also been recorded from Connecticut, Massachusetts, and New Hampshire. Hypericum majus hybridizes also with H. mutilum, with subsp. mutilum in Maine, and with subsp. boreale in Michigan and Wisconsin.