Plant 397

Tulbaghia species (Amaryllidaceae)

Society garlic

The genus Tulbaghia is endemic to southern Africa and contains 20-30 species, with a concentration of species in the Eastern Cape of South Africa. These species inhabit rocky grasslands and stream banks in semi-desert to boggy areas. Ecological differences appear to be correlated with patterning on the outer surfaces of the seeds. Species from dry habitats have seed coats with cells capable of taking up water quickly, whilst those from wet habitats have seed coats with cells that appear impermeable to water.

Tulbaghia species are stemless with underground storage organs and basal, strap-like leaves that often die back during dry seasons. Volatile sulphur-containing compounds, especially marasmin, are responsible for the characteristic garlic-like smell and taste of Tulbaghia species. When underground parts, leaves and flowers are damaged, marasmin is broken down an enzyme to marasmicin, which readily decomposes into an odoriferous cocktail of sulphur compounds.

The main morphological differences among the species are floral form. Flowers have distinctive tissue flaps, associated with their petals, that form a ‘crown’ towards the centre. The genus has been the subject of detailed cytological investigation since the 1960s. Most Tulbaghia species have 12 large chromosomes in each cell, although there are also species with 24 and 36 chromosomes. Moreover, the detailed microscopical appearances of these chromosomes have been used to group and differentiate species, although preliminary DNA analyses suggest chromosome-based classifications need more detailed investigations.

Outside southern Africa, species such as Tulbaghia violacea have been cultivated as perennial garden novelties, especially in dry, well-drained situations. However, for centuries, Tulbaghia species have been used as medicine, food, fodder and ornamentals in their African native ranges. Recently, the belief that Tulbaghia consumption does not taint the breath has seen the promotion of society garlic as a garlic substitute. The medicinal properties of Tulbaghia species that have been used in traditional medicine in South Africa have become the subject of much orthodox medicinal interest, particularly as sources of antimicrobials, cardiovascular drugs and antioxidants. Extracts of Tulbaghia violacea kill a broad range of bacteria, including Staphylococcus and potentially tuberculosis, and nematode worms. Tulbaghia violacea and Tulbaghia alliacea both show distinctive antifungal activities with the potential to make cheap fungicides. Tulbaghia violacea has also been shown to have antioxidant properties and positive effects on high blood pressure.

Carolus Linnaeus (1707-1778) commemorated his correspondent and Governor of the Dutch Cape Colony (South Africa), Ryk Tulbagh (1699-1771) in the generic name Tulbaghia.

Aremu AO et al. 2013. The genus Tulbaghia (Alliaceae) – a review of its ethnobotany, pharmacology, phytochemistry and conservation needs. Journal of Ethnopharmacology 149: 387-400.

Stafford GI et al. 2016. The first phylogenetic hypothesis for the southern African endemic genus Tulbaghia (Amaryllidaceae, Allioideae) based on plastid and nuclear DNA sequences. Botanical Journal of the Linnean Society 181: 156-170.

Vosa CG 2000. A revised cytotaxonomy of the genus Tulbaghia (Alliaceae). Caryologia 53: 83-112.

Stephen Harris