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):

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, 3^rd English ed. Stuttgart: medpharm Scientific Publishers and Boca Raton, FL: CRC Press; 2004:81–83.

Youngken HW. Text-Book of Pharmacognosy, 5^th ed. Philadelphia, PA: The Blakiston Company; 1943:495–499.

Figure 4: a–b, Agathosma betulina leaf and close-up; c, A. crenulata.