Invasive Species and Wildlife Corridors

Oxford Ragwort Senecio squalidus

Recently I have become aware of PlantTracker which has been set up by the Environment Agency, the Nature Locator team at Bristol University and the Centre for Ecology and Hydrology. They are asking for help from the public to track down non-native species that are a threat to our native wildlife. It is well known how species such as Rhododendron ponticum, Fallopia japonica (Japanese Knotweed) and Crassula helmsii (New Zealand Pigmyweed) have become unwelcome aliens in our Country. There is a website and an app for use on smartphones to help locate the plants. The results are already proving to be of help to them and to the BSBI in identifying key risk sites for further invasion problems.

I well remember the excitement back in the 1970s that the late Dr Francis Rose showed when he first found Crassula helmsii in a small pond adjacent to Hatchet Pond in the New Forest. His excitement was caused by the fact that his initial identification of it was Elatine hydropiper, a very rare species that he had never seen before. Further research however put him right, and the truth was that he had had his first encounter with a most unpleasant alien. It did not take long for the whole of the bottom of that pond to be a one species carpet of Crassula helmsii with some important species crowded out completely.

The first occurrence of Crassula helmsii in the New Forest was recorded by the late and very able, deaf botanist Paul Bowman. His notebook showed that having found Crassula helmsii nearby, he then drove to Hatchet Pond. Circumstantial evidence suggests very strongly that a small piece of the plant may well have attached itself to his boot. This shows just what an invasive threat this species must be. The original source of the invasion is thought to have been an aquarist supply shop in Essex.

The story of Oxford Ragwort Senecio squalidus is fascinating. This species is now ubiquitous on the tops of walls and throughout Britain’s railway system. It is now completely taken for granted as part of the British flora. It is called Oxford Ragwort because it was grown in Oxford Botanic Gardens in the late 17th century having been collected from volcanic cinders on the slopes of Mount Etna. It was a small hop from its flower bed in Oxford to the walls of the Botanic Garden from whence it found the walls in the rest of the City and, from 1844, the cinders on the early railway tracks passing through the town. In no time at all, it had established itself throughout Britain on its fast expanding railway network.