Hypericum gymnanthum

Engelmann & A. Gray
Boston J. Nat. Hist. 5: 212. 1845.
Common names: Small-flowered St. John’s wort
Synonyms: Hypericum canadense var. cardiophyllum R. Keller H. mutilum var. gymnanthum (Engelmann & A. Gray) A. Gray Sarothra gymnantha (Engelmann & A. Gray) Y. Kimura
Treatment appears in FNA Volume 6. Treatment on page 93. Mentioned on page 89.

Herbs annual, usually erect, sometimes shortly decumbent and rooting, basal branches none, rarely with 1–3(–6) pairs of narrowly ascending branches distally, 0.6–7 dm. Stems: internodes 4-angled. Leaves spreading, sessile or amplexicaul; blade usually ovate-triangular to broadly ovate, rarely oblong (mid and distal blades lanceolate-deltate), 5–25 × 3–12 mm, papery to membranous, margins plane, apex usually subacute, basal veins (3–)5, midrib usually with 1–2 pairs of branches. Inflorescences laxly corymbiform to cylindric, (1–)5–65-flowered, branching mostly dichasial. Flowers 4.5–7 mm diam.; sepals lanceolate to narrowly ovate, equal, 3–5 × 0.8–1.2 mm, margins sometimes ciliate, not setulose-ciliate, apex acute to acuminate; petals bright yellow, oblanceolate, 2–4 mm; stamens 10–14, scarcely grouped; styles 0.5–0.7 mm; stigmas broadly capitate. Capsules narrowly conic-ellipsoid, 3–5 × 1.5–2 mm, usually broadest at or near middle. Seeds 0.5–0.6 mm; testa finely linear-scalariform. 2n = 16.


Phenology: Flowering summer (Jun–Sep).
Habitat: Bogs, ditches, open and cleared woods, damp habitats
Elevation: 0–400 m

Distribution

V6 157-distribution-map.jpg

Ala., Ark., Del., Fla., Ga., Ill., Ind., La., Md., Miss., Mo., N.J., N.C., Ohio, Pa., S.C., Tenn., Tex., Va., Central America (Guatemala), introduced Atlantic Islands (Azores).

Discussion

Hypericum gymnanthum was introduced into Poland; it is now extinct there. It is closely related to H. mutilum; it differs from that species in the broader, usually deltate leaves; fewer, stricter branches; no condensed apical stem internode; and larger flowers with lanceolate to ovate sepals.

Hybrids of Hypericum gymnanthum with H. mutilum have been reported from Maryland, Mississippi, North Carolina, Tennessee, and West Virginia, and, perhaps erroneously, with H. canadense from Virginia.

Hypericum gymnanthum has clearly been introduced (recently?) into the Azores, not necessarily by man. Seeds may well have been carried there by birds.

Selected References

None.

Lower Taxa

None.

... more about "Hypericum gymnanthum"
Norman K. B. Robson +
Engelmann & A. Gray +
Small-flowered St. John’s wort +
Ala. +, Ark. +, Del. +, Fla. +, Ga. +, Ill. +, Ind. +, La. +, Md. +, Miss. +, Mo. +, N.J. +, N.C. +, Ohio +, Pa. +, S.C. +, Tenn. +, Tex. +, Va. +, Central America (Guatemala) +  and introduced Atlantic Islands (Azores). +
0–400 m +
Bogs, ditches, open and cleared woods, damp habitats +
Flowering summer (Jun–Sep). +
Boston J. Nat. Hist. +
Hypericum canadense var. cardiophyllum +, H. mutilum var. gymnanthum +  and Sarothra gymnantha +
Hypericum gymnanthum +
Hypericum sect. Brathys +
species +