Hypericum majus
Hypericum boreale
greater Canada St. John's-wort, greater Canadian St. John's-wort, large Canadian St. John's-wort, large St. John's wort, millepertuis majeur
millepertuis bor é al, northern bog St. John's-wort, northern St. John's-wort
internodes 4-angled.
internodes 4-angled, apical internode shorter than adjacent one or almost absent.
spreading, sessile or distal subamplexicaul;
blade lanceolate to narrowly oblong-elliptic or (proximal) oblanceolate, 10–45 × (2–)6–12 mm, papery to membranous, margins plane, apex acute to rounded, basal or near-basal veins (3–)5–7, midrib with to 4 pairs of branches.
spreading, sessile;
blade (concolor), broadly to narrowly oblong or elliptic to oblanceolate or round, 5–15 × 2–5 mm, papery to membranous, margins plane, apex rounded, basal veins 3–5, midrib branched or not.
corymbiform to cylindric, 3–30-flowered, usually compact, branching mostly dichasial.
cylindric to rounded-pyramidal, 1–13-flowered, branching mostly dichasial;
bracts not linear-subulate.
6–7 mm diam.;
sepals 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.
3–5 mm diam.;
sepals usually lanceolate to narrowly oblong, rarely oblanceolate, equal, 2.5 × 0.8–1 mm, margins sometimes ciliate, not setulose-ciliate, apex rounded;
petals pale yellow, oblong, 1.7–3.5 mm;
stamens 5–16, scarcely grouped;
styles 0.5 mm;
stigmas broadly capitate.
narrowly conic-ellipsoid, 4–8 × 2.5–3.5 mm, broadest proximal to middle.
narrowly ovoid to cylindric-ellipsoid, 4–5 × 2–2.5 mm, usually broadest at or near middle.
0.5–0.7 mm;
testa finely linear-scalariform.
0.4–0.7 mm;
testa finely linear-scalariform.
= 16.
= 16 [“18”].
Hypericum majus
Hypericum boreale
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.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Where Hypericum boreale grows submerged, the plants are almost always sterile with elongated stems and suborbiculate leaves (H. boreale forma callitrichoides Fassett). Such plants intergrade shorewards with typical H. boreale (F. H. Utech and H. H. Iltis 1970). All other chromosome counts for H. mutilum and its near relatives have given n = 8; B. M. Kapoor’s (1972) count of 2n = 18 must be treated with reserve.
Hypericum mutile var. boreale (Britton) E. P. Bicknell is not a validly published name.
The discovery of Hypericum boreale near the mouth of Fraser River at Vancouver in 1989 extends the distribution of this species across Canada almost to the Pacific coast; this occurrence is almost certainly the result of recent introduction.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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