Cirsium dissectum × C. palustre (C. × forsteri (Sm.) Loudon)
Account Summary
Rare, but very probably over-looked and perhaps occasional.
1884; Barrington, R.M.; Belleisle House, Upper Lough Erne.
Cirsium × forsteri is by far the more common of the two Cirsium hybrids that have been recorded in Ireland and it is the most common thistle hybrid in the British Isles as a whole (W.A. Sledge, in: Stace 1975). Both parents are wetland species, although of the two, C. dissectum is the less frequent and widespread and grows in a more restricted range of habitats (K.J. Walker, in: Stace et al. 2015). Having just remarked on the relative frequency of this thistle hybrid, in the New Atlas it is represented in only 20 Irish hectads and just six of these have post-1986 dates. In NI, it has only been noted twice before in Co Londonderry (H40) and those records are prior to 1938 (FNEI 2).
After it was found by Barrington at Belleisle, as noted above, C. × forsteri was recorded a further seven times in Fermanagh by other recorders working in the 1946-60 period. Regrettably, along with several other more frequent hybrids, it has been overlooked by the current author (RSF) and RHN, and by other field recorders during the last half of the 20th century and first decade of the 21st. It is important that we indicate and acknowledge such gaps in our knowledge of the flora of the county. There is a significant amount of work required to remedy this lacuna.
The parent species quite frequently occur together and the New Flora of the BI (1997) describes C. × forsteri as, "not uncommon with the parents throughout the range of C. dissectum". As is often the case, this hybrid is intermediate between its parents and is not completely sterile. It is described by K.J. Walker in Stace et al. (2015) as, "a distinctive hybrid with decurrent, weakly lobed, sinuate-pinnatifid leaves which, as in C. dissectum, are densely arachnoid-hairy abaxially [ie beneath]". The stem leaves are said by Walker to be, "more spiny and deeply cut than those of C. dissectum, with decurrent spiny wings on the stem, which has a dense indumentum of arachnoid hairs. The 1-3 capitula are intermediate in size and the phyllaries have the viscid callosity below the terminal spines characteristic of C. palustre.".
There is probably little in the way of barriers to hybridisation since the two species flower at the same time in a range of lowland, damp habitats including peaty soils on bog margins, swamps, wet grasslands, dune slacks and even on relatively dry limestone slopes, as in the Burren, Co Clare (H9).
Apart from the first record listed above, six records were made by Meikle and co-workers, and the last one to date by Miss Nora Dawson. The Meikle records were described as coming from cut-over bog, wet pastures and meadows. The other details are: damp pasture, NW of Knockmore, July 1946; Gubbaroe Point, Lower Lough Erne, 1947; Mount Sedborough Lough, 1949; drained lake marked on OS map of 1900, near Lough Slug, 1951; unnamed lake in Tullyvocady Td, 1946-53; meadows above Ross Lough, 1946-53; and shores of Lough Formal, 1950-60, Miss Dawson.
Fermanagh Occurence
References
Cirsium × forsteri is by far the more common of the two Cirsium hybrids that have been recorded in Ireland and it is the most common thistle hybrid in the British Isles as a whole (W.A. Sledge, in: Stace 1975). Both parents are wetland species, although of the two, C. dissectum is the less frequent and widespread and grows in a more restricted range of habitats (K.J. Walker, in: Stace et al. 2015). Having just remarked on the relative frequency of this thistle hybrid, in the New Atlas it is represented in only 20 Irish hectads and just six of these have post-1986 dates. In NI, it has only been noted twice before in Co Londonderry (H40) and those records are prior to 1938 (FNEI 2).
After it was found by Barrington at Belleisle, as noted above, C. × forsteri was recorded a further seven times in Fermanagh by other recorders working in the 1946-60 period. Regrettably, along with several other more frequent hybrids, it has been overlooked by the current author (RSF) and RHN, and by other field recorders during the last half of the 20th century and first decade of the 21st. It is important that we indicate and acknowledge such gaps in our knowledge of the flora of the county. There is a significant amount of work required to remedy this lacuna.
The parent species quite frequently occur together and the New Flora of the BI (1997) describes C. × forsteri as, "not uncommon with the parents throughout the range of C. dissectum". As is often the case, this hybrid is intermediate between its parents and is not completely sterile. It is described by K.J. Walker in Stace et al. (2015) as, "a distinctive hybrid with decurrent, weakly lobed, sinuate-pinnatifid leaves which, as in C. dissectum, are densely arachnoid-hairy abaxially [ie beneath]". The stem leaves are said by Walker to be, "more spiny and deeply cut than those of C. dissectum, with decurrent spiny wings on the stem, which has a dense indumentum of arachnoid hairs. The 1-3 capitula are intermediate in size and the phyllaries have the viscid callosity below the terminal spines characteristic of C. palustre.".
There is probably little in the way of barriers to hybridisation since the two species flower at the same time in a range of lowland, damp habitats including peaty soils on bog margins, swamps, wet grasslands, dune slacks and even on relatively dry limestone slopes, as in the Burren, Co Clare (H9).
Apart from the first record listed above, six records were made by Meikle and co-workers, and the last one to date by Miss Nora Dawson. The Meikle records were described as coming from cut-over bog, wet pastures and meadows. The other details are: damp pasture, NW of Knockmore, July 1946; Gubbaroe Point, Lower Lough Erne, 1947; Mount Sedborough Lough, 1949; drained lake marked on OS map of 1900, near Lough Slug, 1951; unnamed lake in Tullyvocady Td, 1946-53; meadows above Ross Lough, 1946-53; and shores of Lough Formal, 1950-60, Miss Dawson.