Download PDF
Plantago afra
L., P. arenaria Waldst. & Kit.,
P. asiatica
L.,
P. ovata Forssk.
Standardized Common
Name: Psyllium
Other Common Names: Black Psyllium (P. afra, P. arenaria), Blonde Psyllium (P.
ovata), Ispaghula (P. ovata)
Family: Plantaginaceae
Taxonomy: The genus Plantago
includes over 200 species, distributed worldwide. The species used as psyllium
are chosen because they possess unusually mucilaginous seeds; they are not all
closely related. Plantago asiatica belongs to Subg. Plantago. Plantago
afra and P. arenaria belong to Subg. Psyllium, which is the
source of much taxonomic confusion. As traditionally defined, it includes fewer
than twenty species characterized by branched stems with opposite leaves, while
other species have alternate leaves or only basal leavea. Plantago ovata
was until recently classified within Subg. Albicans, but recent
molecular studies have suggested that that subgenus should be combined with
Subg. Psyllium.
Both P. afra and P. arenaria
have P. psyllium L. as a synonym, because Linnaeus applied that name at
various times to different plants (the reason why use of the name is now
avoided, although it has not at this date been formally rejected). Plantago
arenaria is often referred to in literature as P. indica L., but that
name is illegitimate. Plantago afra is not listed in Herbs of
Commerce, although it is one of the major official species in Europe and
elsewhere, perhaps due to the confusion engendered by P. psyllium. It is
very similar to P. arenaria, but is a distinct species. The best-known
synonym for P. ovata is P. ispaghula Roxb. ex Fleming.
Description (species
of Subg. Psyllium): Herbaceous; leaves opposite on stems up to 80 cm high
(in basal rosettes in P. ovata); stems usually pubescent. Leaves linear,
usually <10 cm long, pubescent; primary venation reduced to a single midrib;
margins entire or slightly and irregularly toothed. Inflorescences spicate,
axillary or borne on long basal scapes in P. ovata; peduncle more or
less pubescent; fertile portion dense, bracteate, <3.5 cm long. Flowers
small, whitish to greenish; sepals 4, with green central stripe and apex,
scarious margins; petals 4, fused, dry, pale; stamens 4, basally fused to
corolla, longer than corolla; ovary 2-loculed. Fruit a circumscissile capsule;
seeds 2.
Plantago
asiatica
is most closely related to P. major L. (q.v.) and is very similar
in appearance.
Parts
in Commerce:
Seed
Identification:
- 1.5–3.5 mm long
- More or less
flattened, breadth exceeding depth; “boat-shaped” except in P. asiatica,
with one side convex and one side strongly concave with uprolled margins
- Concave side
bears a pale circular scar (hilum) near the center
- Variable in
color, not black
- Swell and
produce mucilage when put in water
- Taste weak,
mucilaginous
The
official species have several morphological differences:
|
|
P.
afra
|
P.
arenaria
|
P.
asiatica
|
P.
ovata
|
|
Shape
|
Boat-shaped,
ovate to narrowly ovate or oblong
|
Boat-shaped,
oblong to ovate or elliptical
|
Elliptical,
flattened, often somewhat irregular
|
Boat-shaped,
ovate to elliptical
|
|
Length
|
1.3–3.0
mm
|
(1.6–)2.0–3.0(–3.3)
mm
|
1.4–2.3
mm
|
2.0–2.6
mm
|
|
Color
|
Light
brown to brown
|
Dark
brown, often reddish; convex surface usually with paler longitudinal streak
in center
|
Yellowish
to brown
|
Variable,
brown to pinkish, reddish or gray-brown, often with darker spot towards one
end of convex surface
|
|
Surface
|
Smooth,
glossy
|
Irregular,
glossy to dull
|
Smooth,
glossy
|
Smooth,
shiny or dull
|
Adulterants: The best way to
distinguish adulteration by cultivated or weedy Plantago species having
inferior mucilage content is to determine the swelling index. This test is
conducted by soaking 1 gram (g) of seeds in a 25 milliliter (ml) graduated
cylinder full of water. In the basic procedure as described by the World Health
Organization, a mixture of plant matter and water is shaken several times over
an hour, then left to stand for a minimum of three hours. However, Youngken
recommended that psyllium should be shaken occasionally over a 24-hour period,
followed by 12 hours left to stand. The volume of the mass of mucilage then
present at the bottom of the cylinder, in ml, is equivalent to the swelling
index. For example, if 1 g of seeds produces 9 ml of mucilage, since 1 ml of
water weighs 1 g, the mucilage weighs roughly 9 g, or nine times the original
weight of the seeds; the swelling index would therefore be 9. Minimum swelling
indices specified by various authorities for the official species range from
8–10, but higher-quality cultivated material has higher values, especially in P.
afra, for which Wichtl reports 14–19 as a typical range.
Accurate description of P. asiatica
presents special problems due to lack of adequate taxonomic study and
information in literature. Western pharmacognostic references state that P.
asiatica has flattened, pale brown seeds up to 2 mm long. However, some
Asian botanical literature indicates that P. asiatica has blackish
seeds, which are occasionally described as multiangled or as little as 1 mm
long. A variety of seed shapes and colors are observed in herbarium material
labeled as P. asiatica. This appears to be due in part to
misidentification of P. major, which can appear extremely similar to P.
asiatica. Seeds of P. major are small, irregularly shaped and
dark-colored, sometimes with a pattern of thin dark striations. Seeds of that
appearance are probably not genuine P. asiatica. Substitution of P.
major can be detected by determination of the swelling index.
A historical adulterant reported by
Youngken is the seed of Lallemantia royleana Benth. (a member of the
mint family), which had a swelling index of 40, or 47–50 after 48 hours, higher
than would be expected of intact psyllium seeds. The seeds of Lallemantia
can also be recognized morphologically by their shape. One side is flat, while
the other side has a very prominent longitudinal ridge (so that the seeds are
T-shaped in cross-section). They are glossy dark brown with a whitish bump
(hilum) at one end of the longitudinal ridge; the margins may be transparent.
References:
Chater AO, Cartier D. Plantago. In: Tutin TG, Heywood VH, Burges NA, et al.,
eds. Flora Europaea. Vol. 4. Cambridge: Cambridge University
Press; 1976:38–44.
Liu J-Z, Zhang Q-M, Guo S-H, Zhou X-D. 1992. Seed
morphology of Plantago in China and its taxonomic significance. [In
Chinese] Acta Phytotax Sinica. 1992;30:118–125.
Ohwi J. Flora of Japan (in English).
Washington, DC: Smithsonian Institution; 1965.
Panigrahi G. A note on Plantago exigua (Plantaginaceae)
and certain related taxa. Kew Bull. 1975 [publ. 1976];30:669–673. [For
nomenclature of P. arenaria.]
Rahn K. Nomenclatorial changes within the genus Plantago
L., infraspecific taxa and subdivisions of the genus. Bot. Tidsskr.
1978;73:106–111.
Rahn K. Plantago ser. Ovatae. A
taxonomic revision. Bot Tidsskr. 1979;74:13–20.
Rahn K. A phylogenetic study of the Plantaginaceae. Bot
J Linn Soc. 1996;120:145–198.
Rezk MR. Seed structure as a phylogenetic criterion:
a case of Plantago seed. Egypt J Bot. 1980;23:51–62.
Rønsted N, Chase MW, Albach DC, and Bello MA.
Phylogenetic relationships within Plantago (Plantaginaceae):
evidence from nuclear ribosomal ITS and plastid trnL-F sequence data. Bot.
J. Linn. Soc. 2002;139:323–328.
Wichtl M, ed. Herbal Drugs and
Phytopharmaceuticals, 3rd English
ed. Stuttgart: medpharm Scientific Publishers and Boca Raton, FL: CRC Press;
2004:461–463 and 478–479.
World Health Organization. 1998. Quality Control
Methods for Medicinal Plant Materials. Geneva: World Health Organization;
1998.
World Health
Organization. WHO Monographs on Selected Medicinal Plants. Vol. 1. Geneva: World Health Organization;
1999–2002:202–212.
Youngken HW. Text-Book of Pharmacognosy, 5th ed. Philadelphia, PA: The
Blakiston Company; 1943:801–810.
Figure 56: a, seed of Plantago afra; b, seed of P. major
misidentified as P. asiatica.
