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Geum rivale × G. urbanum (G. × intermedium Ehrh.), Hybrid Avens

Account Summary

Occasional and very local.

1884; Barrington, R.M.; N end of White Island, Eastern Lower Lough Erne.

March to June.

The Fermanagh distribution of this relatively frequent fertile intermediate hybrid closely reflects that of its less widespread parent G. rivale (Water Avens), or rather the overlap in distribution and habitats of the two parent species. It is claimed that the frequency of the hybrid in the area of the parent species overlap is positively influenced by disturbance (Taylor 1997a), which would tend to bring the more weedy G. urbanum (Wood Avens) into greater contact with the natural wet ground species, G. rivale. While this may be generally true, only three of the 18 or more distinct sites known for this hybrid in a total of 17 Fermanagh tetrads might conceivably be considered public enough to fit this pattern (eg the Crom Castle and Florencecourt National Trust estates and the Cladagh River Glen NR).

The ecological separation of the two parent species is not the whole story, since in the very mild, damp climate of W Ireland, the flowering periods of these Geum species certainly overlap more than they do in drier, more continental climatic conditions (Briggs & Walters 1997, p. 282). These circumstances also pertain at the much larger scale of B & I and the New Atlas map shows that this hybrid is much more frequent in NI than elsewhere on the island.

The Irish Flora Census Catalogue indicates that G. × intermedium has been recorded at least once in 19 of the 40 Irish VCs (Scannell & Synnott 1987), a figure which we can revise upwards to 24 thanks to the New Atlas map (Preston et al. 2002).

G. × intermedium is fully fertile and it can therefore backcross with both parents, sometimes displaying an array of forms intermediate in character between the parents which are typically both present in the near vicinity, ie it forms a hybrid swarm with a continuous linking range of intermediates between the two parent species.

While it is relatively frequent in some VCs, although still always very local, eg in Fermanagh and Co Antrim (H33, H39)(Hackney et al. 1992), in the Flora of County Dublin (H21), it was described as extremely rare, there being just one record dating from 1983 (Doogue et al. 1998).

As with G. rivale, the New Altas survey suggests that there have been some losses, particularly in C & S England, presumably due to drainage and other factors responsible for destruction of damp, shady habitats (D.J. McCosh, in: Preston et al. 2002).

Fermanagh Occurence

Threats

None.