Utricularia minor L., Lesser Bladderwort

Native, scarce and local. Circumpolar boreo-temperate.

1806; Scott, Prof R.; Co Fermanagh.

June to October.

This species occurs in very similar habitats to U. intermedia s.l. (Intermediate Bladderwort) and the two are sometimes found together in drains or shallow pools on peat bogs (including on cut-over bogs) and in acidic, nutrient-poor, oligotrophic, mainly upland lakes. In Fermanagh, it has been recorded in 33 tetrads, 6.3% of the VC total, but only 23 of them have post-1975 records. U. minor remains widely but thinly scattered throughout most of Fermanagh, being more prevalent on the western and northern plateau bogs and lakes. The species losses that the tetrad map highlights probably are real, and while the upland bogs and lakeshores Lesser Bladderwort chiefly frequents are less likely to be affected by agricultural intensification 'improvements', drainage associated with peat extraction and with forestry, together with widespread eutrophication through agricultural and urban or domestic household nutrient run-off, remain potential threats in the more accessible sites in Fermanagh.

Like U. intermedia s.l., U. minor also has two kinds of submerged branches or stolons, one with green floating leaves and one colourless with reduced leaves. The colourless stolons often act as anchors, attaching the floating plant to the underlying substrate. In this instance, and unlike U. intermedia, both types of branch bear insect-trapping bladders (Garrard & Streeter 1983; An Irish Flora 1996).

U. minor is only very occasionally found in flower throughout much of its B & I range. It flowers from June to September, the flowering stems projecting about 8 cm above water. The corolla is a very pale yellow, 7 mm long and with a very short, blunt spur (An Irish Flora 1996). The spur is so short it has been described as 'slight' (Melderis & Bangerter 1955). The frequency of flowering varies greatly from year-to-year and U. minor flowering occurs much more regularly in Scotland than for other species of the genus (Preston & Croft 1997). In common with all other Utricularia species in B & I, however, reproduction is largely achieved vegetatively, by formation of leafy buds called 'turions' which develop on the end of the green stolons from late July onwards. These dormant buds overwinter and germinate the following spring.

Lesser Bladderwort is fairly frequent in the peatlands of the N and W of both Ireland and Britain and it has been recorded in every Irish VC except Co Dublin (H21) (Cen Cat Fl Ir 2). The hectad map for the species in Preston & Croft (1997), however, highlighted the marked decline and, indeed, extinction of U. minor in many southern and eastern VCs in both B & I, and this pattern of decline has been confirmed by the New Atlas survey (F.J. Rumsey, in: Preston et al. 2002). Having said this, it is commonly acknowledged that all species of Utricularia and, indeed, probably all submerged aquatic plant species are undoubtedly under-recorded to some extent (Preston & Croft 1997; Sell & Murrell 2009).

The major reason for the losses of U. minor is the direct destruction of peat bogs in more accessible lowland areas, through drainage and peat cutting. However, a secondary source of loss is through simple neglect of bogland areas across the country, with consequent scrub encroachment onto bog surfaces, the shading effect of which would also contribute to Bladderwort species decline. A further hazard affecting Utricularia species has arisen from the widespread intensification of agriculture since the 1950s, with increased mechanisation of drainage operations and annually repeated application of artificial fertilisers and/or organic slurry, inevitably resulting in chemical runoff and giving rise to eutrophication of water bodies. Atmospheric pollution, especially that involving nitrogen oxides, and particulate waste from urban sources and fumes from transport, also contribute to nutrient enrichment and eutrophication, acting both directly and indirectly against the survival of aquatics through increasing competition from algae and other aggressive, more vigorously responsive associated species.