Sisymbrium orientale L., Eastern Rocket

Account Summary

Growth form, origin and history of introduction

S. orientale is an alien neophyte annual that was first recorded as introduced to Britain in the early 18th century as a contaminant of imported grain, very probably including hen food. It is a native of N Africa, Macaronesia, the Near East to W Himalaya and S Europe from Portugal to Bulgaria and Turkey (Garrard & Streeter 1983; Jalas & Suominen 1994, Map 2123). It has been widely introduced elsewhere in both hemispheres, including to B & I and on the coast of Norway to 68N. It has been repeatedly reintroduced to B & I in more recent times along with wild bird food seed and also as a sheep wool adventive (Salisbury 1964, p. 141; Clement & Foster 1994). S. orientale was not recorded in Ireland until the very end of the 19th century (Cat Alien Pl Ir).

Irish occurrence and preferred habitats

Although it can commonly become naturalised in parts of SE England, in Ireland, Eastern Rocket is regarded as a casual spring or winter annual which in NI only rarely becomes more or less naturalised in docks, roadsides, railways, waste ground and other disturbed, open, well-illuminated, moderately dry to mesic soil habitats, including on and around walls (FNEI 3; Urban Flora of Belfast; Hill et al. 1999). On account of this strong habitat association with commerce, transport and large urban areas in general, S. orientale is more frequently recorded in eastern Ireland, although it really is only regarded as a fairly common casual. Reynolds (2002) lists it as having been recorded at least once from 25 of the 40 Irish VCs.

A very much better estimate of the species Irish occurrence is demonstrated in the New Atlas, where the hectad map displays records of S. orientale very thinly scattered on this side of the Irish Sea. Of the approximately 83 hectads of any age-class plotted for Ireland, 35 are from east coast or nearby districts.

Fermanagh occurrence

S. orientale first appeared in Fermanagh in 1951 in a football ground car park close to a railway yard. The railway is long gone, having closed in autumn 1957. The second of our four VC records was made by RHN exactly 40 years later, also on waste ground in Enniskillen town. This very clearly indicates just how rare a casual it is in our area. The two remaining records were also made by RHN at Old Crom Castle in 1995 and 1999, when the plant was found growing quite abundantly on a wall at one spot and subsequently on disturbed ground just north of the castle.

British occurrence

Eastern Rocket is very much more common in Britain than in Ireland, at least in the area S of a line between Liverpool and Hull, and there is a similar widespread representation around the large Scottish conurbation of Glasgow and Edinburgh (Preston et al. 2002). S. orientale appears to have first come into prominence during the 1940s Blitz in London, where and when, along with many other ruderal species, it rapidly colonised vacant bomb sites (Salisbury 1964).

In Britain, and possibly also in the Dublin and Belfast urban areas, S. orientale appears to have spread considerably during the last 50 years. In Britain at least, its status has graduated to it becoming 'a persistent casual' (Rich 1991; D.A. Pearman, in: Preston et al. 2002).

Biology

The main period of germination is in autumn, the young plant overwintering as a small leaf rosette with a slender tap-root (Clapham et al. 1962). Flowers are produced over a long season, from May to September or even longer in warmer, milder parts of these islands (Rich 1991; An Irish Flora 1996). However, apart from this observation and mention by Rich (1991) that the flowers are self-incompatible (no reference quoted), the current author has been unable to locate any further information regarding the reproductive biology or population behaviour of the species. S. orientale is resistant to some herbicides. Clearly little or nothing is known of the seed biology, since the species does not appear in either the meta-survey of soil seed bank data for NW Europe (Thompson et al. 1997), nor in the germination trials of Grime et al. (1981). It thus appears that Eastern Rocket is a subject where school project observations in areas of B & I where the plant is more common, might add worthwhile data to the basic biology of the species.

Threats

None, since it is a very rare casual.

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