Utricularia intermedia Hayne s.l. (ie U. intermedia s.s., U. ochroleuca R.W. Hartm. and U. stygia G. Thor), Intermediate Bladderwort
Account Summary
Native, rare and probably declining. Circumpolar boreal-montane.
1806; Scott, Prof R.; Scottsborough near Magheraveely.
July to September.
This complex of three poorly known aquatic species which occur in similar situations is typically, but in Fermanagh rather rarely found, in shallow, still or slow-moving nutrient-poor, oligotrophic water in peaty sites, including the edges of bogland pools and ditches, or free-floating and submerged in upland lakes. In many instances, it is not free-floating, but rather is anchored to the underlying substrate by its colourless, trap-bearing stolons. None of the local Fermanagh records are from wet moorland flushes, although the aggregate is said to occur in this habitat elsewhere in B & I (Preston & Croft 1997).
As noted with the other Utricularia species so far mentioned, members of the U. intermedia aggregate flower very infrequently, even less so than U. vulgaris s.l. or U. minor (Lesser Bladderwort). Reproduction is thus heavily reliant upon the production of vegetative turions (leafy buds) which usually begin to develop on the green stolons in late July or August, or even earlier when in shallow water bodies prone to drying out (Preston & Croft 1997).
Fermanagh occurrence
U. intermedia was one of the first 18 species ever recorded in Fermanagh in 1805 by Prof Scott, who with this record, made the initial discovery of the species (or species complex) in the British Isles (Mackay 1806; Praeger 1949).
There are a total of 24 records for Intermediate Bladderwort from 15 tetrads in the Fermanagh Flora Database. There were four records of the plant prior to the 1946-53 survey by Meikle and co-workers. Their work produced an additional seven records on the Western Plateau (Revised Typescript Flora). Considering the amount of wetland survey work carried out in Fermanagh since 1975, there are relatively few recent records – a total of just 13. The plant has only once been found by the current author (RSF) & RHN. Thus while there are records from 15 tetrads in Fermanagh, only six of these have post-1975 dates and, as the distribution map shows, the taxon remains very thinly scattered throughout the VC.
British and Irish occurrence
As the New Atlas hectad map indicates, U. intermedia s.l. is predominantly a species complex of the cooler, wetter, more acidic NW parts of B & I. In Ireland, it is thinly scattered, but mainly occurs down the West coast from Cos Donegal, Fermanagh, Galway to Kerry and Cork. There are very few recent records of U. intermedia s.l. from anywhere in NI (FNEI 3).
In Britain, it is widely scattered in N & W Scotland, while in England it is very rare and sparsely scattered further south, but mainly occurs in Cumbria and S C England, East Anglia and in Caernarvonshire in NW Wales (F.J. Rumsey, in: Preston et al. 2002; Sell & Murrell 2009). It is believed that U. intermedia s.l. may well be over-recorded for U. ochroleuca (Sell & Murrell 2009).
The observed decline of the species complex in B & I is probably explained by a loss of habitat through lowland peat areas being drained, together with the eutrophication of pools and ditches associated with artificial fertiliser and/or slurry run-off from farmland. It has to be recognised, however, that since the species of this complex are completely submerged aquatics that grow in brown peaty waters, they are very easily overlooked, and the possibilities of their under-recording and mis-identification are all too obvious.
European and world occurrence
U. intermedia s.l. has a Circumpolar boreal-montane distribution and in Europe it is considered frequent in the boreal zone, extending south in scattered locations to S France and N Italy (Preston & Croft 1997).
References
Preston & Croft 1997; Mackay 1806; Praeger 1949; Revised Typescript Flora; FNEI 3; New Atlas; Sell & Murrell 2009.