Wild radish (Raphanus raphanistrum)

Wild radish (Raphanus raphanistrum) is a winter and spring-growing annual with somewhat unusual four-petaled flowers which vary in colour and venation. The species would have arrived in Australia as a contaminant in seed wheat or other field grain or vegetable (eg. brassica) seed; it was first recorded in South Australia in 1879, and in Melbourne in 1885. It is a superadapted weed to grain and vegetable cultivation: in addition to being difficult to process out of seed wheat when it does get collected with the seed crop, it has number of other adaptations. It generally grows to flowering quite quickly, and then drops its seeds prior to the maturity of competing crops, facilitating its persistence in local field systems. Wild radish also benefits from complex seed dormancy which ensures its re-emergence over a number of years, outlasting any short-lived effort at control. The plant is a capable allelopathic suppressor of germination, emergence and seedling growth of some crop species as well as potential competitor weeds; meanwhile it has been documented that populations of the weed in WA have developed resistance to a broad spectrum of herbicides. It is declared as a noxious weed in parts of NSW, and is also a documented environmental weed throughout Australia, particularly in riparian zones and disturbed woodlands. The photographed plants were growing on the flood banks of the Yarra River and Merri Creek, in the vicinity of the confluence at Dights Falls, and showcase the plant’s variable flower colouring.