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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, 8th 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, 5th 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.
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