Hypericum mutilum L.

Dwarf St. John's-Wort


CC = 4
CW = -3
MOC = 78

© SRTurner

Family - Hypericaceae

Habit - Annual or short-lived perennial forb, fibrous rooted, sometimes with a rhizomelike creeping basal portion of the stem, this rooting at the nodes.

Stems - Loosely ascending to erect, to 90 cm, rounded or inconspicuously angled or ridged below each leaf, green.

Hypericum_mutilum_stem.jpg Stem and leaves.

© SRTurner

Leaves - Opposite, often decussate, sessile. Leaf blades 4-40 mm long, 1-15 mm wide, lanceolate, ovate, or elliptic, rounded or bluntly pointed at the tip, broadly angled to rounded or shallowly cordate at the base, often somewhat clasping and crowding the stem, the margins flat, membranous to herbaceous in texture, with mostly 3 or 5 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.

Hypericum_mutilum_leaf1.jpg Leaf adaxial.

© SRTurner

Hypericum_mutilum_leaf2.jpg Leaf abaxial.

© SRTurner

Inflorescence - Panicles of 5-60 flowers at branch tips, usually more or less rounded in outline, sometimes reduced to small clusters of flowers at the branch tips.

Hypericum_mutilum_inflorescence.jpg Inflorescence.

© SRTurner

Flowers - Actinomorphic. Sepals 5, all similar in size and shape, 2-4 mm long, usually becoming slightly enlarged at fruiting, linear-lanceolate to narrowly oblong-lanceolate, lacking noticeable yellowish brown or black dots, lines, and/or streaks. Petals 5, 1.5-2.5 mm long, narrowly oblong to oblong-oblanceolate, bright yellow to lemon yellow, lacking noticeable dark markings, usually shed by fruiting. Stamens 5-16, the filaments sometimes irregularly spaced but usually not fused into groups. Ovary 1-locular, with parietal placentation. Styles 3, free above the base, more or less spreading, the stigmas capitate

Hypericum_mutilum_calyx.jpg Calyx.

© DETenaglia

Hypericum_mutilum_flowers.jpg Flowers.

© SRTurner

Hypericum_mutilum_flower.jpg Flower.

© SRTurner

Fruits - Capsules 2-4 mm long, at maturity usually slightly longer than the sepals, ellipsoid, widest at about the midpoint, narrowed or short-tapered to the persistent styles, more or less circular in cross-section. Seeds numerous, 0.4-0.7 mm long, the surface with a faint network of fine ridges and pits, appearing inconspicuously longitudinally ribbed to nearly smooth, light brown to brown.

Hypericum_mutilum_fruits.jpg Fruits.

© SRTurner

Flowering - July - October.

Habitat - Banks of streams, ponds, and sloughs, bottomland forests, swamps, ditches, moist areas.

Origin - Native to the U.S.

Lookalikes - Other members of the genus Hypericum.

Other info. - This small species of St. John's wort is found across nearly all of Missouri, except the far northwestern corner of the state, and across the eastern half of the continental U.S. It is easy to recognize by its sessile opposite leaves, small yellow flowers, and wet habitat. If held up to the light, leaves of all species of Hypericum will be seen to be dotted with tiny, translucent spots (usually called "pellucid dots"). In this species, the leaves also have tiny yellowish to black glandular dots, which are visible on the abaxial surface photo above.

Hypericum mutilum has been subdivided into three subspecies. Missouri material is referable to ssp. mutilum Look for it in areas where spring waters have slowly receded, leaving behind muddy banks or flats.

Photographs taken at Pultite Spring, Shannon County, MO., 7-23-04 (DETenaglia); also at Port Hudson Conservation Area, Franklin County, MO, 8-28-2014, and Klondike County Park, St. Charles County, MO, 7-30-2016 (SRTurner).