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Frangula
purshiana (DC.) J. G. Cooper
Standardized Common
Name: Cascara Sagrada
Other Common Names: Cascara, Chittam
Bark, Sacred Bark
Family: Rhamnaceae
Taxonomy: Frangula
includes a dozen species that are segregated from Rhamnus based on
several shared morphological features (cf. Rhamnus cathartica L.).
Both genera are widely distributed in the Northern Hemisphere. When Frangula
and Rhamnus are combined into a single genus, the correct name for this
species is Rhamnus purshiana DC. It is native to the northwestern United
States, extending to California, Arizona and western Canada.
Description: Large shrub to small
tree, (1–)3–10(–15) m tall. Trunk 15–50(–90) cm in diameter, usually dividing
into multiple branches within 3–5 m, irregularly branching. Bark gray to dark
reddish brown, smooth to longitudinally furrowed or scaly, especially at base
of trunk. Young twigs greenish, softly pubescent; older twigs reddish-brown and
nearly glabrous; winter buds lacking bud scales, no terminal bud present.
Leaves alternate and clustered at ends of twigs, stipulate with stipules small and quickly lost, petiolate; blade
elliptical to ovate, oblong-ovate or obovate, (2.5–)5–18(–20) cm long; base
obtuse to cordate; apex variable, acute to obtuse or rounded; margins nearly
entire, usually minutely serrate, often undulate; venation pinnate, with 9–16
pairs of secondary veins, curving forward near margins, conspicuous beneath;
lower surface paler than upper, somewhat pubescent. Inflorescences lateral,
cymose. Flowers small (3–4 mm in diameter), bisexual or unisexual, greenish;
sepals 5, basally fused; nectar disk present inside calyx; petals 5; stamens 5,
opposite petals rather than alternating with them; ovary 2–4-loculed, with 1
ovule per locule. Fruit a drupe, berry-like, 6–12 mm in diameter, black or
purplish black at maturity, with 3 (2–4) pyrenes.
Parts
in Commerce:
Bark, usually aged for at least a year
Identification:
- 1–4(–6) mm thick
- Occurs in broad,
nearly flat pieces (from trunk) or curved pieces or quills 0.5–2.0 cm wide
(from branches); frequently processed into small cut pieces
- Outer surface
commonly bearing irregular flattened coating of white to grayish lichen
and occasionally growths of moss or liverworts, with brownish to reddish cork
visible beneath when scraped; otherwise, brown to purplish or reddish
brown, often longitudinally ridged
- Lenticels absent
or present, pale, elongated, with the long axis perpendicular to the
branch or trunk
- Inner surface of
bark yellowish when fresh, often pale reddish brown or purplish-brown
after drying, longitudinally striated or barely ridged
- In
cross-section, contains brownish or purplish external cork (10 or more
cell layers thick); narrow yellowish-brown to yellowish-gray cortex; thick
yellowish-brown secondary phloem
- If observed with
a light microscope, cortex and outer portion of phloem contain calcium
oxalate crystals and pale, irregularly shaped or roughly elliptical
clusters of thick-walled sclereids; secondary phloem in transverse section
contains numerous parenchyma rays (perpendicular to surface, (1–)2–4(–5)
cells thick, irregularly curving) and short narrow bands of fibers
parallel to surface (these features cannot be seen clearly with a
dissecting microscope)
- Fracture short,
somewhat fibrous in inner portion, with broken fibers projecting from
surface of inner bark
- Odor weak,
characteristic
- Taste bitter and
nauseating; tinges saliva yellow
The
inner surface produces a reddish color when treated with a drop of dilute
alkali (lye) or ammonia solution.
Adulterants: Frangula
californica (Eschsch.) A. Gray, or Rh. californica Eschsch.
(California Coffeeberry), once considered to be a variety of F. purshiana,
has the longest history of any Frangula or Rhamnus species from
the western United States. The two plants are very similar, and material of “F.
purshiana” from southern California frequently contains F. californica.
Frangula californica has broader parenchyma rays in the phloem, and the
inner surface of the cork cambium, the thin growing layer immediately below the
cork, is crenate rather than nearly flat. (These characters are not readily
observed without the use of a light microscope.) Twigs tend to remain densely
pubescent to a later stage of growth than those of F. purshiana, and
remains of hairs may be visible even on rather large branches.
Frangula
alnus
Mill. (Frangula):
The bark of this European species, also known as Rh. frangula L.,
differs from F. purshiana in several features:
- Bark always
<2 mm thick
- Outer surface
variable in color; when scratched, exposed inner cork is deep crimson or
purple
- Lenticels
numerous, sometimes rounded
- Inner surface
yellowish to dark red with purple blotches or brown
- No clusters of
stone cells present in cortex; calcium oxalate crystals present
- Taste only
weakly bitter, mucilaginous
This
species likewise produces a reddish color when the inner surface is moistened
with an alkaline solution, as would other species containing the same active
compounds.
References:
Bolmgren K, Oxelman B. Generic limits in Rhamnus
s.l. (Rhamnaceae) inferred from nuclear and chloroplast DNA sequence
phylogenies. Taxon. 2004;53:383–390.
Elias TS. The Complete Trees of North America.
Field Guide and Natural History. New York, NY: Gramercy Publishing Co.;
1987.
Evans WC. Trease and Evans’ Pharmacognosy, 14th ed. London: WB Saunders
Company Ltd.; 1996:239–242.
Hayes DW, Garrison GA. Key to Important Woody
Plants of Eastern Oregon and Washington. Washington, DC: U. S. Department
of Agriculture; 1960. Agriculture Handbook, No. 148.
Hickman JC, ed. The Jepson Manual: Higher Plants
of California. Berkeley: University of California Press; 1993.
Kraemer H. The medullary ray cells in Rhamnus
Purshianus. J Am Pharm Assoc. 1912;1:846–849.
Taylor RL, Taylor S. Rhamnus purshianus in
British Columbia. Davidsonia. 1980;11:17–23.
World Health
Organization. WHO Monographs on Selected Medicinal Plants. Vol. 2. Geneva: World Health Organization;
1999–2002:259–268.
Youngken HW. Text-Book of Pharmacognosy, 5th ed. Philadelphia, PA: The
Blakiston Company; 1943:551–560.
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