Rubus idaeus × R. caesius (R. × pseudoidaeus (Weihe) Lej.)
Account Summary
Native, very rare.
1948; MCM & D; Scottsborough, near Magheraveely.
Fermanagh occurrence
This hybrid between two of the more commonly identified brambles in B & I, the Raspberry (R. idaeus) and the Dewberry (R. caesius), has only been recorded once in Fermanagh as listed above. While R. idaeus (both wild and cultivated) has been recorded frequently and widely in Fermanagh, R. caesius is rare, having only been found on eleven occasions in the VC, although it is very probably under-recorded (see the R. caesius species account).
Hybrid identification
The parent species are very different in many respects, but their hybrid resembles R. caesius in habit and stem characters. The leaves are closer to those of R. idaeus, but mostly with 3-5 leaflets and the inflorescence is short and corymbose (Newton, A., in: Stace 1975). Hybrid plants with ternate leaves can be distinguished from R. caesius by having pubescent carpels, curled hairs on the abaxial leaf surface (ie the under-surface) and reddish-black fruits (if formed). Hybrid plants with five or seven leaflets per leaf can be distinguished from R. idaeus by having leaves only loosely hairy on the under-surface, the stipules are broader, flowers have larger petals and, again, the fruit colour is reddish-black. The flowers of hybrid plants can be either white or pink (Stace et al. 2015).
British and Irish occurrence
Edees & Newton (1988) commented that hybrids of R. caesius with brambles of Section Corylifolii are probably frequent and, indeed, this whole bramble Section possibly arose as a result of crossing between R. caesius and Section Rubus. This could mean that up to 200 European bramble taxa originate from pairings with R. caesius. Nevertheless, Newton (in: Stace 1975), regarded R. caesius × idaeus as fairly rarely recorded in B & I and in his own subsequent book he listed a total of just nine English VCs from which records of the hybrid were known (Edees & Newton 1988).
The hectad map in The Hybrid Flora of the British Isles plots just two hectads with records of this hybrid in Ireland, one in Fermanagh and the other in N Tipperary (H10). However, for Britain, the same map plots 35 widely scattered hectads where the hybrid has now been recorded (Stace et al. 2015). With just one exception, where R. × pseudoidaeus was accompanied by R. idaeus only, the hybrid is always recorded in the presence of both parent species. The habitats where the parents coexist are listed as woods, hedgerows, wooded railway banks, commons and rough grasslands, roadside banks and the sides of ditches (Stace et al. 2015).
Cytology
R. idaeus is a sexual diploid species (2n=14 (mostly)), while R. caesius is either a tetraploid (2n=28), or a pentaploid apomict (2n=35) (A. Newton, in: Stace 1975). The F1 hybrid is, therefore, largely infertile (2n=35 (mostly) but the figure can range as follows: 21, 28, 35, 42) (Stace et al. 2015). As the F1 generation is not completely sterile, later generations do exist and backcrosses with the parent species are said to occur (A. Newton, in: Stace 1975).