Senecio jacobaea × S. aquaticus (S. × ostenfeldii Druce), a ragwort hybrid
Account Summary
Native, very rarely recorded but probably often over-looked.
1938; Praeger, R.Ll.; Co Fermanagh.
Praeger mentioned this hybrid as being present in Fermanagh in his book, The Botanist in Ireland, without giving any locality. He regarded this plant as common all over Ireland (Praeger 1951), although he clearly had a very good eye for spotting it, a better one than anyone else since! He believed it commonly formed large populations in neglected marshy pastures. To date, S. × ostenfeldii has only been recorded twice in the VC since Praeger's first mention of it in Fermanagh, both finds being made by Meikle and his co-workers in 1949. Their site details are: lakeshore pasture, Drumcose Lough, Ely Lodge Forest; and by Tempo River near Shanco Td.
Certainly, this biennial or short-lived perennial hybrid must have been regularly overlooked recently, since both parents are abundant and widespread in the county. The hybrid is said to generally occur along with its parents in damp, disturbed grasslands and it should be looked out for in such sites.
The hybrid plant is very variable in morphology, although intermediate between its parents. Being partially fertile, hybrid swarms occur and apparently these may sometimes become very large, so that the two species completely intergrade.
Like S. aquaticus (Marsh Ragwort), the hybrid possesses a large terminal leaf lobe and produces a few-flowered corymb. It resembles S. jacobaea (Common Ragwort) in its much-cut upper leaves (Harper & Wood 1957). Other features are described in Hybridization (p. 405) and in the Hybrid Flora (Stace et al. 2015).
References
The Botanist in Ireland; Praeger (1951); Harper & Wood (1957); Hybridization; Stace et al. (2015)