Hypericum ×mitchellianum
Hypericum boreale
Blue Ridge St. John's wort
millepertuis bor é al, northern bog St. John's-wort, northern St. John's-wort
internodes usually 2-lined, sometimes 4-lined or not lined, with black glands scattered on and near lines or all over.
internodes 4-angled, apical internode shorter than adjacent one or almost absent.
spreading, usually sessile, rarely petiolate (to 0.8 mm);
blade ovate-oblong to oblong or elliptic, 30–42(–52) × 8–22 mm, base subcordate to rounded, margins plane, apex usually rounded, rarely obtuse or subretuse, midrib with 4–5 pairs of branches, tertiary veins densely reticulate toward margins, black glands intramarginal (dense) and laminar (scattered).
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 broadly pyramidal, (5–)13–61(–124)-flowered, subsidiary branches narrowly ascending or curved-ascending.
cylindric to rounded-pyramidal, 1–13-flowered, branching mostly dichasial;
bracts not linear-subulate.
15–20 mm diam.;
sepals not imbricate, erect in fruit, lanceolate to ovate-elliptic or elliptic, subequal, (3–)3.6–4.6(–5.5) × 1–2 mm, apex acute to obtuse;
petals golden yellow, narrowly obovate or oblanceolate to elliptic, 6–11 mm;
stamens (37–)42–56(–62);
anther gland black;
styles 1.5–5 mm.
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.
ellipsoid to subglobose, 3–7 × 3–4.5 mm, with longitudinal vittae.
narrowly ovoid to cylindric-ellipsoid, 4–5 × 2–2.5 mm, usually broadest at or near middle.
not carinate, 0.7–0.9 mm;
testa not seen.
0.4–0.7 mm;
testa finely linear-scalariform.
= 16.
= 16 [“18”].
Hypericum ×mitchellianum
Hypericum boreale
Hypericum ×mitchellianum is intermediate in all characters between H. graveolens and H. punctatum and, like the latter, produces a ring of 16 chromosomes at meiosis (D. E. Culwell 1970). Culwell has shown that it hybridizes with H. graveolens in the field and that these species can be crossed artificially. He apparently never suspected that H. mitchellianum could itself be a hybrid. Its intermediate morphology and breeding behavior, together with a distribution almost wholly within that of H. graveolens, suggests strongly that H. mitchellianum is the hybrid H. graveolens × punctatum, which apparently arose when the area of H. punctatum extended into that of H. graveolens.
(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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