Scutellaria lateriflora L.

Standardized Common Name: Skullcap

Other Common Names: Blue Pimpernel, Helmet Flower, Mad-dog Skullcap, Scullcap

Family: Lamiaceae (Labiatae)

Taxonomy: Scutellaria includes about 360 species of herbs and small shrubs, found almost worldwide. About 240 of these, including S. lateriflora, are placed within subgenus Scutellaria, section Scutellaria, which is probably not a natural group and has been divided (by Paton) into numerous informal species groups. Several of these are native to eastern North America; morphological diversity among species is great enough to allow most to be identified without difficulty.

Description: Perennial, rhizomatous herb. Stems 30–60(–80) cm high, quadrangular, varying along stem from purplish-brown to yellowish-green; lower part unbranched and glabrous, upper part with opposite branches and bearing small appressed hairs and sometimes glands. Leaves opposite, petiolate with petioles 0.5–3 cm long, narrowly ovate to ovate or ovate-oblong, 3–7 cm long, 2–3.5 cm broad; base acute to rounded-truncate or subcordate; apex acute; margins serrate to somewhat crenate or dentate; upper surface dark; lower surface pale, pubescent with tiny appressed hairs along veins and many glandular hairs; venation pinnate, reticulate. Inflorescences racemose, 3–8 cm long, mostly lateral, sometimes terminal, one-sided, with opposite solitary flowers subtended by small leaflike bracts. Calyx at flowering 1.5–2.5 mm long, campanulate-bilabiate, toothed, membranous, pale green, bearing small hairs and occasionally glands; upper lip folds to form scutellum, at maturity expanding to enclose fruits. Corolla 5–9 mm long, tubular-bilabiate, blue or rarely white or pink, slightly pubescent at least outside; lateral lobes more closely joined to upper lip than to lower; lower lip larger, upper lip hooded and concealing anthers. Stamens 4, in 2 pairs. Ovary deeply 4-lobed; fruit 4 nutlets, ca. 1 mm long, pale brown, ellipsoidal, wrinkled, enclosed within “helmet-shaped” calyx.

Parts in Commerce: Whole herb at flowering (stems, leaves, flowers)

Identification:

• Stems quadrangular, mostly 1–4 mm in diameter, glabrous to sparsely pubescent or glandular above, not densely pubescent
• Leaves 3–7 cm long, with toothed margins
• All leaves petiolate
• Leaf bases variable, but not strongly cordate or asymmetrical
• Upper leaf surface glabrous or nearly so
• Lower leaf surface sparsely pubescent with short appressed hairs, especially along veins, and bearing numerous multicellular, short-stalked glands
• Inflorescences racemose, mostly lateral, with flowers all borne to one side in pairs
• Bracts beneath flowers leaflike, but smaller than leaves
• Upper lip of calyx with a conspicuous projection (scutellum)
• Corolla bilabiate, with lower lip longer than upper lip; upper lip hooded, the stamens mostly or entirely contained within the corolla
• Corolla <10 mm long
• Corolla bluish (rarely white or pink)
• Stamens 4, in 2 pairs, the filament bases attached to the corolla tube (above the midpoint in the upper pair); filaments often ciliate
• Fruits, if present, consist of 4 nutlets enclosed within an enlarged asymmetrical calyx

Adulterants: The unusual shapes of the calyx and corolla easily identify flowering material as belonging to the genus Scutellaria. American skullcaps that have appeared in commerce include S. ovata Hill, S. incana Spreng., and S. galericulata L. (also known as S. epilobiifolia A. Hamilt., its common names of Common Skullcap or Hooded Willow-herb, the latter shared by S. lateriflora, may have led to confusion). The above points distinguish S. lateriflora from these and all other potentially confused species, including S. churchilliana Fern., which is thought to be a hybrid involving S. laterifolia. If the material is sufficiently intact, the observation of one-sided lateral racemes and small (<10 mm) flowers is virtually diagnostic.

Skullcap has been found to be adulterated with Teucrium canadense L. (American Germander), which is a serious safety issue as germander has been shown to be hepatotoxic. T. canadense is also known as Pink Skullcap, increasing the likelihood of confusion with Scutellaria. However, it can be easily distinguished by several features:

• Upper lip of corolla is split and its lobes fused with the prominent lower lip so corolla appears to have no upper lip
• Stamens protrude from cleft in upper side of corolla
• Calyx symmetrical, not forming a scutellum
• Leaf bases sometimes asymmetrical
• Both leaf surfaces and stem pubescent; lower leaves sometimes densely pubescent with non-glandular hairs

References:

Epling C. 1942. The American species of Scutellaria. Univ Calif Publ Bot. 1942;20:1–146.

Fernald ML. Gray’s Manual of Botany, 8^th ed. New York: American Book Company; 1950:1217–1223.

Paton A. A global taxonomic investigation of Scutellaria (Labiatae). Kew Bull. 1990;45:399–450.

Youngken HW. Text-Book of Pharmacognosy, 5^th ed. Philadelphia, PA: The Blakiston Company; 1943:737–739.

Figure 65: a–d, Scutellaria lateriflora habit, flower, stem and fruit; e–g, Teucrium canadense flower, leaf and fruit.