5. Hypericum gymnanthum Engelm. & A. Gray (clasping-leaved St. John’s wort, small St. John’s wort)

Pl. 360 g–i; Map 1565

Plants annuals, with taproots. Stems 15–70 cm long, erect, rounded or inconspicuously angled or ridged below each leaf, green. Leaves not jointed at the base, spreading to loosely ascending. Leaf blades 5–30 mm long, 3–12 mm wide, lanceolate-triangular to ovate-triangular, rounded or bluntly or occasionally sharply pointed at the tip, broadly rounded to shallowly cordate at the base, often somewhat clasping the stem, the margins flat, herbaceous to slightly leathery in texture, with mostly 5 or 7 main veins from the base, the surfaces with inconspicuous, minute, yellowish brown to dark green or black resinous dots, the upper surface green, the undersurface somewhat paler, not glaucous. Inflorescences appearing as panicles of 5–50 flowers, usually more or less flat-topped in outline. Flowers actinomorphic. Sepals 5, all more or less similar in size and shape, 3.5–5.0 mm long, usually becoming slightly enlarged at fruiting, lanceolate, lacking noticeable yellowish brown or black dots, lines, and/or streaks. Petals 5, 3–4 mm long, oblanceolate, bright yellow to lemon yellow, lacking noticeable yellowish brown or black dots, lines, and/or streaks, usually shed by fruiting. Stamens 10–15, the filaments sometimes irregularly spaced but usually not fused into groups. Ovary 1-locular or appearing partially 3-locular by intrusion of the parietal placentae into the locule. Styles 3, free above the base, more or less spreading, the stigmas narrowly capitate. Fruits 3–5 mm long, at maturity about as long as the sepals, narrowly ovoid, widest well below the midpoint, tapered to the persistent styles, more or less circular in cross-section. Seeds numerous, 0.5–0.6 mm long, the surface with a faint network of ridges and pits, appearing inconspicuously longitudinally ribbed to nearly smooth, light brown to brown. 2n=16. June–September.

Uncommon and widely scattered in the southern third of the state (eastern U.S. west to Kansas and Texas; disjunct in Guatemala, introduced in Europe). Margins of ponds and sinkhole ponds, banks of streams, and upland prairies and sand prairies, usually in moist depressions; also pastures, fallow fields, and ditches.

Steyermark (1963), Robson (1990), and others have noted the presence of putative hybrids between H. gymnanthum and H. mutilum where these two species occur together. Such hybrids have been recorded thus far from Shannon and Texas Counties and are to be expected nearly everywhere that H. gymnanthum is found in Missouri. Hybrid plants, which are difficult to distinguish from the parents, tend to have smaller flowers with less-tapered sepals than those of H. gymnanthum and less strongly triangular leaves.