Hypericum sphaerocarpum
Hypericum ×mitchellianum
round-fruit St. John's-wort, roundseed St. Johnswort
Blue Ridge St. John's wort
internodes 2–4-lined.
internodes usually 2-lined, sometimes 4-lined or not lined, with black glands scattered on and near lines or all over.
blades narrowly elliptic or narrowly oblong to linear, 30–70 × 3–15 mm, base not articulated, narrowly cuneate to linear, margins plane to revolute, apex subacute to rounded, midrib with 0–4 pairs of branches.
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).
rounded-corymbiform, 7–70-flowered, narrowly branched, sometimes with dichasia or branches from to 8 proximal nodes.
corymbiform to broadly pyramidal, (5–)13–61(–124)-flowered, subsidiary branches narrowly ascending or curved-ascending.
10–15 mm diam.;
sepals persistent, not enclosing capsule, 5, broadly ovate to oblong-elliptic, ± unequal, 2.5–5 × 1.5–3 mm;
petals 5, bright yellow, oblanceolate-elliptic to elliptic, 5–9 mm;
stamens persistent, 45–85;
ovary 3-merous, placentation parietal.
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.
broadly ovoid to depressed-globose, 4.5–8 × 4–7 mm.
ellipsoid to subglobose, 3–7 × 3–4.5 mm, with longitudinal vittae.
carinate, 2–2.7 mm;
testa coarsely reticulate.
not carinate, 0.7–0.9 mm;
testa not seen.
= 16.
Hypericum sphaerocarpum
Hypericum ×mitchellianum
Hypericum sphaerocarpum differs from H. cistifolium and H. nudiflorum in its semiherbaceous habit and more northwestern distribution, as well as in its combination of relatively long, narrow leaves, persistent sepals, globose and apiculate to rounded capsules, and relatively large seeds. The narrow-leaved, bushy form from eastern parts of the range (var. turgidum) merges with the typical form.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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.)
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