Standardized Common Name: St. John’s Wort

Other Common Name: Klamath Weed

Family: Hypericaceae or Clusiaceae (Guttiferae)

Taxonomy: Hypericum is a widespread and very diverse genus of about 450 species, divided into about 30 sections and ranging from herbaceous weeds to large trees. H. perforatum is the type species of Sect. Hypericum, which includes 52 herbaceous species. The species is native to Eurasia, where it may have originated through hybridization between H. maculatum Crantz and H. attenuatum Choisy. The best taxonomic treatment recognizes four subspecies of H. perforatum, of which only subsp. perforatum (Europe and North America) and subsp. veronense (Schrank) H. Lindb. (Europe and Southwest Asia) are widely distributed. Considerable intergradation exists between these subspecies in Europe.

Description: Perennial herb; stems (20–)30–70(–100) cm high, branching, clustered at base, tough, with 2 raised longitudinal ridges, bearing small dark glands. Leaves opposite, sessile or subsessile, elliptic to linear-oblong, (5–)10–30(–35) mm long, 2–10 mm wide, with translucent glandular dots; apices obtuse; margins entire. Inflorescences cymose, leafy, many-flowered. Sepals narrowly lanceolate, 3–4 mm long, glandular-punctate; apex acute to acuminate or attenuate. Petals orange-yellow, obovate, 10–12 mm long, often slightly toothed at apical end on one side, with black dots on the margin and occasional black streaks. Stamens numerous, grouped in 3(–5) clusters, 6–8 mm long. Styles 3(–5); ovary of 3(–5) fused carpels. Fruit a septicidal capsule, 6–8(–10) mm long, ovoid, with elongated apex. Seeds numerous, brown to blackish, glossy, with netted ridges on surface.

Parts in Commerce: Whole herb

Identification:

Stem

• With 2 longitudinal lines, not with 4 lines or wings or round
• Hairless
• With few small black glandular dots on lines

Leaves

• Pale green
• Oblong to elliptical or linear, mostly 10–30 mm long
• Secondary veins curving to become parallel over most of leaf length, with inconspicuous netted tertiary venation between
• Glands in blade usually pale, conspicuous below; occasionally with a few black dots
• Hairless
• Petiole very short or absent
• Leaf base rounded to tapering, or cordate and somewhat clasping in one Asian subspecies
• Margins entire, often slightly revolute, with few small black glands near apex

Sepals

• 5, 3–4 mm long, narrow
• Surface has clear glandular spots; black dots or streaks absent or sparse
• Lacking elongated oil vesicles
• Margins usually entire, with no or few black glands

Petals

• 5, 10–12 mm long, obovate
• Orange-yellow, with darker veins
• Few black dots near margin, sometimes with black dots or streaks or pale glands elsewhere on surface

Stamens

• Numerous, borne in 3 bundles (very rarely in 5)
• Filaments long, narrow, yellowish
• Black glands present on anthers

Adulterants: Several European species of Hypericum have been found as adulterants. All of these, as well as similar American species, can be distinguished morphologically. Hybridization between H. maculatum and H. perforatum is known to occur in eastern Europe, and a series of intermediates exists. H. maculatum is characterized by:

• Stem lines 4
• Leaves with few or no clear glandular dots
• Leaf veins conspicuously netted
• Sepals broader and somewhat toothed
• Petals with few black dots along the margins but with numerous black dots and streaks elsewhere on the surface

First-generation hybrids are intermediate in form, often having 2 conspicuous and 2 weak lines on the stem. Gene flow between the two species is probably uncommon but of longstanding natural occurrence.

References:

Mártonfi P, Repčak M, Mihoková L. Hypericum maculatum Crantz subsp. maculatum ×H. perforatum L. (Hypericaceae): Corroboration of natural hybridization by secondary metabolite analysis. Folia Geobot Phytotax. 1996;31:245–250.

Robson NKB. Hypericum. In: Tutin TG, Heywood VH, Burges NA, et al., eds. Flora Europaea. Vol. 2. Cambridge: Cambridge University Press; 1968:261–269.

Robson NKB. Studies in the genus Hypericum L. (Guttiferae) 4(2). Section 9. Hypericum sensu lato (part 2): subsection 1. Hypericum series 1. Hypericum. Bull Nat Hist Mus Lond (Bot). 2002;32:61–123.

Robson NKB. Hypericum botany. In: Ernst E, ed. Hypericum: the Genus Hypericum. London: Taylor & Francis; 2003:1–22. Medicinal and Aromatic Plants—Industrial Profiles, vol. 31.

Wichtl M, ed. Herbal Drugs and Phytopharmaceuticals, 3^rd English ed. Stuttgart: medpharm Scientific Publishers and Boca Raton, FL: CRC Press; 2004:305–308.

Figure 33: Hypericum perforatum habit, flower and leaf.