The main 'weed' species is the native Common ragwort (Senecio jacobaea) which thrives where bare ground or thin vegetation allows the development of seedlings. The plant is often biennial, with rosettes forming in the first year that later (usually the next year) develops into a flowering shoot which can tolerate being among other tall vegetation. Common ragwort supports the most specialist insect species, however the native Hoary ragwort (Senecio erucifoliusci) which is similar in appearance, is also preferred by some insects.
 Chris Hatfield Small skipper and cinnabar moth.jpg) |
| Small skipper butterfly and Cinnabar caterpillar on ragwort © Chris Hatfield |
The New Atlas of the Flora of Britain and Ireland (2002) shows Ragwort as native and states that ‘the distribution of Ragwort is unchanged from the map in the 1962 Atlas’. In addition, the Countryside Survey (a national scientific study) found no specific evidence of an increase in Ragwort in grasslands (i.e. grazing land) during the period 1990 to 1998. Although they showed an increase in lowland woods and on arable land, neither of these habitats are frequently grazed by horses. The perceived increase in Ragwort abundance seems to be simply a result of increasing awareness.
There are also other widespread Ragworts with similar sized flowers which look similar to common ragwort. Marsh ragwort (Senecio aquaticus), occurs locally in wet, unimproved fields. The growth form is shorter and the flowering shoots are more splayed than Common ragwort. Current information suggests that this supports fewer species of special insects but remains important for pollinating insects. Oxford ragwort (Senecio squalidus) is an introduced plant, with a loosely bushy growth form, which has become very widespread as a weed along railway lines and on rubbish dumps. A few insects feed upon it, but it is more important as a nectaring source for insects.
Additionally there are some rare native Senecio notably the Fen ragwort (Senecio paludosus), which grows to 2m in height, and the Welsh groundsel (Senecio cambrensis), a species of waste ground and waysides.
Most of the other widespread native species of Senecio are groundsels. These often have inconspicuous flowers with poorly developed petals, whereas Ragworts have larger bright yellow petals. Groundsels support a relatively poor fauna however the Sticky groundsel (Senecio viscosus) is used by a few specialist species and is mildly attractive to pollinating insects.
It is important to realise that there are numerous other plants with a roughly similar growth-form and yellow flowers. Even on the ground, with limited botanical knowledge it is possible to be confused as to whether plants are Ragworts or not, let alone which Ragwort species. Tansy (Tanacetum vulgare), St. John's Wort (Hypericum spp.) and Hawkweeds (Hieracium spp.) are among the plants commonly mistaken for Ragwort.
