Agathosma betulina (P. J. Bergius) Pillans,
A. crenulata
(L.) Pillans, A. serratifolia
(Curtis) Spreeth
Standardized Common
Name: Buchu
Other Common Names: Boegoe, Ibuchu
Family: Rutaceae
Taxonomy: Agathosma
includes about 150 species of shrubs, all native to South Africa, which are
highly variable in chemistry and scent. Several are used medicinally; A.
betulina, A. crenulata and A. serratifolia are used
interchangeably as Buchu according to Herbs of Commerce. The latter two
are very similar, and authorities disagree as to whether they should be
considered two different species or a single species. According to van Wyk et
al., A. crenulata is less desirable than A. betulina due to
higher pulegone content. The two species hybridize and intermediate forms may
be observed. These species were formerly placed in the genus Barosma,
which is now lumped into Agathosma, and the synonyms B. betulina
(P. J. Bergius) Bartl. & H. L. Wendl., B. crenulata (L.) Hook., and B.
serratifolia (Curtis) Willd. are still frequently encountered in
literature.
Description: Shrubs to 2 m high;
twigs often with reddish bark in long strips, with minutely papillate and
glossy appearance. Leaves opposite, small, short-petioled, glabrous, conspicuously
glandular-dotted beneath; margins toothed with inconspicuous glands between
teeth and at apex. Flowers solitary, axillary, on short pedicels; sepals 5,
2.5–3.5 mm long, with slightly ciliate margins; petals 5, 7–10 mm long, white
to pink or mauve; stamens 5; filaments pubescent below, attached to a
cup-shaped disk that surrounds the ovary; sterile, glandular-tipped staminodes
present; ovary 5-lobed; style 1, recurved, pubescent below. Fruit a 5-chambered
capsule, with deep clefts between locules; seeds 1 per locule, glossy black.
Parts
in commerce:
Leaves
Identification: The leaf shape of A.
betulina differs from that of A. crenulata (and A. serratifolia):
|
A. betulina
|
A. crenulata/serratifolia
|
Leaf size
|
(0.7–)1–2 cm long
|
(1–)1.5–3(–4) cm long
|
Leaf shape
|
Broadly obovate to broadly elliptical or rhomboid; length usually not over twice breadth
|
Narrowly elliptical to lanceolate, oblong, ovate or obovate
|
Leaf apex
|
Obtuse usually toothed all the way around and shallowly recurved
|
Obtuse to rounded-truncate, with a visible gland
|
Leaf teeth
|
Shallow, irregular, usually pointed, serrate to dentate
|
Very shallow, usually blunt, crenate to serrate
|
However,
they have a number of features in common:
- Lower surface
pale yellowish green, paler than upper surface, notably
glandular-punctate; glands circular, embedded in leaf tissue, yellowish or
darkened
- Leaves glabrous
on both surfaces (at most, with few tiny hairs along lower part of sunken
midrib on upper surface)
- Texture thick,
surface often slightly wrinkled
- Margins
shallowly toothed; inconspicuous yellow glands present just inside the
notches between leaf teeth
- Midrib raised
and conspicuous beneath; secondary veins few, arcing, often invisible
- Base tapering to
very short petiole
- Odor aromatic, similar
to blackcurrant or mint
- Taste aromatic,
bitter, similar to blackcurrant or camphor
Adulterants: Most of the
previously reported adulterants also belong to Rutaceae (the citrus family),
including other Agathosma species, Empleurum Sol. ex Aiton (which
is used like buchu), Adenandra fragrans (Simms) Roem. & Schult.
(which is used as a tea) and Diosma L. (known as False Buchu). Most
relatives of the preferred species are smaller and have smaller leaves. Agathosma
pulchella (L.) Link has leaves sometimes similar in size to those of A.
betulina, but the teeth are reduced to near zero length, the margins may be
pubescent, there are no conspicuous glands on most of the leaf surface, and the
scent is lemony; the ovary and fruit are usually 3-lobed.
Leaves
of Adenandra fragrans are narrowly oblong to linear, whereas leaves of A.
serratifolia or A. crenulata are more noticeably broader in the
middle than at the base and apex. The margins are more or less entire, minutely
papillose and often thickened and darkened; it has a scent similar to licorice.
Leaves of Empleurum unicapsulare (L.f.) Skeels are of similar shape and
frequently 4–5 mm long; the margins are only minutely toothed but do bear
glands between the teeth. They can be distinguished from the official species
of Agathosma by the apex, which is acuminate with a sharp tip; the
glands on the lower surface are sometimes absent or present in a single row
down each side of the midrib rather than scattered.
Legumes
with glandular-punctate leaves have also been found as adulterants of buchu,
especially Otholobium obliquum (E. Mey.) C. H. Stirt. (reported under
its original name, Psoralea obliqua E. Mey.). Otholobium, like Psoralea,
is pubescent and has raised glandular hairs; the leaf apex bears a short sharp
recurved point (mucron). O. obliquum has trifoliolate leaves whose
obovate leaflets somewhat resemble the leaves of Agathosma; the lateral
leaflets are asymmetrical, the midrib and margins are hairy especially in young
leaves, and the petiole has two small stipules attached.
References:
Bean PA. Agathosma. In: Goldblatt P, Manning
J. Cape Plants: a Conspectus of the Cape Flora of South Africa.
Pretoria: National Botanical Institute and St. Louis, MO: Missouri Botanical
Garden Press; 2000:624–631. Strelitzia, No. 9.
Pillans NS. A revision of Agathosma. J S
Afr Bot. 1950;16:55–183.
Spreeth AD. ‘n Hersiening van die Agathosma-spesies
van kommersiele belang. J S Afr Bot. 1976;42:109–119.
Stirton CH. 1989. A Revision of Otholobium C.
H. Stirton. Ph.D. Dissertation, University of Cape Town. [For adulterant
only.]
van Wyk B-E, van Oudtshoorn B, Gericke N. Medicinal
Plants of South Africa. Pretoria: Briza Publications; 2000.
Wichtl M, ed. Herbal Drugs and
Phytopharmaceuticals, 3rd English
ed. Stuttgart: medpharm Scientific Publishers and Boca Raton, FL: CRC Press;
2004:81–83.
Youngken HW. Text-Book of Pharmacognosy, 5th ed. Philadelphia, PA: The
Blakiston Company; 1943:495–499.
Figure 4: a–b, Agathosma
betulina leaf and
close-up; c, A. crenulata.