Sinapis alba L., White Mustard
Account Summary
Introduction, archaeophyte, an extinct casual. Native distribution has been obscured by long cultivation and wide naturalisation in both hemispheres, but it is probably European southern-temperate.
1903; Praeger, R.Ll.; Belleek village.
Growth form and preferred habitats
A tall (20-100 cm), yellowish-green, annual with deeply lobed upper stem leaves, fibrous roots and pale yellow flowers in dense, crowded racemes. The fruit pod has a flattened terminal segment or beak, 10-30 mm long. There are usually two to three seeds in each swollen loculus of the fruit (Rich 1991). Previously a common weed of arable cultivation, it has declined to become a rare casual of waysides, disturbed ground and gardens, where it is used in wild bird seed feeding mixtures.
Flowering reproduction and physiology
S. alba flowers from May to September and is pollinated by bees and flies. It has been used in physiological experiments on flower induction and, as far as is known, it is unique in being a long day species in which flowering can be induced by just a single exposure to a day-length greater than 10 hours. Under the specified experimental conditions, flowering is maximised by an exposure to an 18 hour day. It was also found that the timing of exposure to light has a considerable influence on the extent of the flowering response and that a single short 8 hour day could also induce flowering provided it fell within the 20 hour circadian period when the species was receptive to a light stimulus promoting anthesis (Kinet 1972).
Fermanagh occurrence
There have been no further records of White Mustard in Fermanagh since Praeger's 1903 find on waste ground in the village of Belleek on the county boundary. While the seed can survive hidden in the soil seed bank for many years, after a century of no sightings we may safely conclude that what was always in earlier days, a casual plant, is now locally extinct in the VC.
British and Irish occurrence
Elsewhere in Ireland, where White Mustard still occurs, it is an even more infrequent or rare casual than was formerly the case (Cat Alien Pl Ir). In Britain, S. alba has also declined over four or more decades (the New Atlas change index is -0.90). However, the species remains very widely scattered as a casual ruderal in lowland areas of these isles. S. alba is more persistent in calcareous soils and in B & I it is only really frequent and abundant in SE England.
In the past, White Mustard was occasionally grown and used by farmers as a green manure, being ploughed in to improve soil fertility. Nowadays, many, and possibly the majority of records of this species, are associated not with arable farming, but with its use in wild bird seed mixtures, used to attract and feed wintertime avian garden visitors. Perhaps this is why it tends to be found mainly on disturbed wayside and waste ground, where it may have been discarded, or escaped from gardens by its own means of dispersal – including by the assistance of feeding birds (Reynolds 2002). Seed of this long cultivated annual is associated with Roman sites in Britain, making it of archaeophyte status (Salisbury 1964, p. 29).
European and world occurrence
As with S. arvensis, the native distribution of White Mustard is entirely obscured by its long history of cultivation and association with man, to the extent that Jalas et al. (1996) do not even attempt to map it in their Atlas Florae Europaeae, 11. In its world distribution, we may say that S. alba is primarily a southern temperate zone European species, possibly native in the Mediterranean basin (Rich 1991). However, S. alba is so very widely introduced and naturalised it has become almost circumpolar in the N Hemisphere (ie it is missing only in E Asia). S. alba is also naturalised in New Zealand (Hultén 1971, p. 6) and in S America and Australia (Rich 1991).
Uses
Grown chiefly for use as a green salad, S. alba was once the mustard of 'mustard and cress' fondly remembered by many people from primary school biology experiments or early 'Nature Table' experiences. Nowadays, however, even this decidedly minor vegetable role has been replaced by Brassica napus (Oil-seed Rape) (Rich 1988). However, commercial mustard preparations do still include the use of seeds of Sinapis alba (White Mustard), mixed along with those of Brassica juncea (Brown Mustard), or rarely with B. nigra (Black Mustard) (Rich 1991; Vaughan & Geissler 1997).
Names
The English common name 'Mustard' is of 13th century origin and is derived from the Old French 'moustarde' and 'mostarde', which referred to seeds of S. alba and Brassica nigra together ground up and mixed with 'moust de vin', that is, with 'must', new wine, a term itself derived from the Latin 'mustum', making a condiment for eating with meat (Grigson 1974).
Threats
None.