Plant 336

Asparagus species (Asparagaceae)


In England, St. George’s Day is the traditional start of the asparagus season, when asparagus spears, the newly emerged shoots of Asparagus officinalis, begin to be eaten as vegetables. In the words of Marcel Proust, these spears, ‘finely daubed with mauve and azure’, when eaten, turn the ‘chamber pot into a perfume vase’.

The distinctive odour of the asparagus-eater’s urine, recorded since at least the sixteenth century, is caused by the cocktail of sulphur-containing compounds produced when asparagusic acid is broken down during digestion. Individuals in human populations vary in their abilities to detect the odour, the result of genetic differences among olfactory receptors. Asparagus lends its name to the amino acid asparagine, which was first isolated from asparagus juice by two French chemists in 1806.

The genus Asparagus, which comprises some 200 species, is naturally distributed through Europe, Asia and Africa where it occupies habitats ranging from rainforests to semi-deserts. Some Asparagus species are woody scramblers with adaptations for using surrounding plants as support. Other species, such as Asparagus officinalis, are herbaceous; their appearance has led to them being inappropriately christened ‘asparagus ferns’ in the horticultural trade. The leaf-like photosynthetic structures of Asparagus are not leaves, they are flattened stems – technically cladodes. The true leaves are reduced to tiny, non-photosynthetic scales at the base of the cladodes. Asparagus roots produce tubers which are used for the storage of water and food reserves.

Asparagus flowers, which are often overlooked, are either male or female and found on separate plants (dioecious). In contrast, Asparagus fruits are small berries whose colours (e.g., red, white and black) contrast starkly with the vegetative parts of the plant. Features that have led to the suggestion Asparagus fruits are dispersed by birds.

In Britain, two subspecies of Asparagus officinalis are recognised. Subspecies officinalis, the familiar garden asparagus, was introduced from Europe and has been a crop (and sometimes a weed) in English fields since at least the seventeenth century. Subspecies prostratus grows wild and is a rare native plant, found in cliff-top vegetation in coastal parts of south-west England and western Wales.

In 2018, approximately 9.1 million tonnes of asparagus was harvested globally; nearly 90% of this was grown in China. In contrast, British production, which is concentrated in parts of eastern England, Worcestershire and Lancashire, was about 5,000 tonnes. Increased popularity of asparagus over the last two decades, has seen annual British production approximately triple.

Further reading

Eriksson N et al. 2010. Web-based, participant-driven studies yield novel genetic associations for common traits. PLOS Genetics 6: e1000993.

Kubota S et al. 2012. Molecular phylogeny of the genus Asparagus (Asparagaceae) explains interspecific crossability between the garden asparagus (A. officinalis) and other Asparagus species. Theoretical and Applied Genetics 124: 345-354.

Zapata et al. 2014. Bird-mediated seed dispersal of fleshy fruits of Mediterranean shrubs in semiarid forest patches: the role of Pinus halepensis Miller trees as seed receptors. Plant Ecology 215: 1337-1350.

Stephen Harris