Hypericum ×mitchellianum

Rydberg

Torreya 27: 84, plate 2, figs. 1 – 6. 1927.

Common names: Blue Ridge St. John’s wort
Endemic
Treatment appears in FNA Volume 6. Treatment on page 101. Mentioned on page 98, 100, 102.

Herbs erect, with rooting, creeping base, 2–6.5 dm. Stems: internodes usually 2-lined, sometimes 4-lined or not lined, with black glands scattered on and near lines or all over. Leaves 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). Inflorescences corymbiform to broadly pyramidal, (5–) 13–61 (–124) -flowered, subsidiary branches narrowly ascending or curved-ascending. Flowers 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. Capsules ellipsoid to subglobose, 3–7 × 3–4.5 mm, with longitudinal vittae. Seeds not carinate, 0.7–0.9 mm; testa not seen. 2n = 16.


Phenology: Flowering summer (Jun–Aug).
Habitat: Open or partly shaded, moist habitats, dry, rocky roadside banks
Elevation: 1100–1700 m

Discussion

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.

Selected References

None.

Lower Taxa

None.
... more about "Hypericum ×mitchellianum"
reddish +  and black +
gland black +
oblong;ellipsoid +
acute;obtuse +
Norman K. B. Robson +
Rydberg +
striate +  and smooth +
punctiform +
distinct +
subcordate +  and rounded +
4.2 cm42 mm <br />0.042 m <br /> (5.2 cm52 mm <br />0.052 m <br />) +
3 cm30 mm <br />0.03 m <br /> (4.2 cm42 mm <br />0.042 m <br />) +
ovate-oblong +  and oblong or elliptic +
0.8 cm8 mm <br />0.008 m <br /> (2.2 cm22 mm <br />0.022 m <br />) +
0.3 cm3 mm <br />0.003 m <br /> (0.7 cm7 mm <br />0.007 m <br />) +
ellipsoid;subglobose +
0.3 cm3 mm <br />0.003 m <br /> (0.45 cm4.5 mm <br />0.0045 m <br />) +
Blue Ridge St. John’s wort +
N.C. +, Tenn. +  and Va. +
1100–1700 m +
connate +  and distinct +
1.5 cm15 mm <br />0.015 m <br /> (2 cm20 mm <br />0.02 m <br />) +
laminar +  and intramarginal +
Open or partly shaded, moist habitats, dry, rocky roadside banks +
(5-)13-61(-124)-flowered +  and corymbiform +
axillary +  and terminal +
not lined +, 4-lined +  and 2-lined +
terete +  and angled +
petiolate +  and sessile +
deciduous +  and persistent +
glandular-ciliate +
3(-4)-merous +
axile +  and parietal +
glanduliferous +
contorted +  and imbricate +
golden yellow +
persistent +
distinct +
oblanceolate;elliptic +
0.6 cm6 mm <br />0.006 m <br /> (1.1 cm11 mm <br />0.011 m <br />) +
Flowering summer (Jun–Aug). +
not carinate +
0.07 cm0.7 mm <br />7.0e-4 m <br /> (?) +  and 0.09 cm0.9 mm <br />9.0e-4 m <br /> (?) +
not imbricate +
0.46 cm4.6 mm <br />0.0046 m <br /> (0.55 cm5.5 mm <br />0.0055 m <br />) +
persistent +
connate +  and distinct +
lanceolate;ovate-elliptic or elliptic +
subequal +
0.1 cm1 mm <br />0.001 m <br /> (0.2 cm2 mm <br />0.002 m <br />) +
persistent +
connate +  and distinct +
elongate +
0.15 cm1.5 mm <br />0.0015 m <br /> (?) +  and 0.5 cm5 mm <br />0.005 m <br /> (?) +
curved-ascending +  and ascending +
Hypericum sect. Concinna +  and Hypericum sect. Graveolentia +
Hypericum ×mitchellianum +
Hypericum sect. Hypericum +
species +
scalariform +
reticulate +  and foveolate +
south +, west +  and north +
hairy +  and glabrous +
6 +, 9 +  and 7 +