Hypericum ×mitchellianum
Hypericum densiflorum
Blue Ridge St. John's wort
bushy St. John's-wort, dense St. Johnswort
internodes usually 2-lined, sometimes 4-lined or not lined, with black glands scattered on and near lines or all over.
internodes 4-lined at first, soon 2-lined to terete.
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).
blades narrowly elliptic-oblong or oblanceolate to linear, 20–45 × 2–7 mm, base articulated, narrowly cuneate to attenuate, margins recurved to revolute, apex apiculate-rounded to subacute, midrib with 14–17 pairs of branches.
corymbiform to broadly pyramidal, (5–)13–61(–124)-flowered, subsidiary branches narrowly ascending or curved-ascending.
broadly pyramidal to broadly cylindric, 5–25-flowered from apical node, with (2–)5–15-flowered dichasia from 1–2 proximal nodes.
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.
10–17(–20) mm diam.;
sepals deciduous, not enclosing capsule, 5, narrowly oblong to oblanceolate-spatulate, unequal or subequal, 4–6 × 1–1.5 mm, basal veins 1–3;
petals 5, deep golden yellow, obovate-oblanceolate, 6–9 mm;
stamens deciduous, 100–150;
ovary 3–4(–5)-merous.
ellipsoid to subglobose, 3–7 × 3–4.5 mm, with longitudinal vittae.
narrowly ovoid conic to cylindric-ovoid, 5–6(–7) × 2–3 mm, not or scarcely lobed.
not carinate, 0.7–0.9 mm;
testa not seen.
not carinate, 0.8–1.3 mm;
testa linear-reticulate.
= 16.
= 18.
Hypericum ×mitchellianum
Hypericum densiflorum
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.)
Hybrid intermediates between Hypericum densiflorum and H. lobocarpum occur in northwestern Alabama, and a narrow-leaved, small-flowered form in Tennessee and northern Georgia (H. interior) verges toward H. galioides. Hypericum densiflorum is always distinct from H. prolificum in the wild; these species hybridize in gardens. Hypericum ×arnoldianum Rehder, known in cultivation only, was thought by Rehder to have the parentage H. galioides × lobocarpum; on both morphological and cytological grounds, the conclusion of W. P. Adams (1972) that it was H. densiflorum × lobocarpum seems much more likely.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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