Utricularia vulgaris L. s.l. (ie both U. vulgaris s.s. and U. australis R. Br.), Greater Bladderwort

Account Summary

Growth form and preferred habitats

This is a submerged, free-floating, rootless, aquatic, with leaves finely divided into linear segments and carrying numerous, tiny, animal-catching 'bladder' traps. Utricularia species are stemless, or almost so, as well as being rootless, the stems being replaced by stolons. The genus contains 215 species and is extremely variable in morphology and in the sheer scale of the plants (Preston & Croft 1997; Sell & Murrell 2009).

U. vulgaris is a perennial of slow-moving or still, base-rich, mesotrophic to oligotrophic water, typically found in sheltered bays around lowland lakes, deep ditches in fens, marshes and in grazed water meadows that flood from time-to-time after heavy rainfall. It can occupy both acidic and basic, highly calcareous water over a range of inorganic or peaty substrate bottoms. It can tolerate a degree of shade, but cannot cope with eutrophic conditions and the level of competition they support. U. vulgaris is affected by eutrophication, benefiting from a little of it, but adversely reacting to excessive nutrient enrichment (George 1992). It is often found in shallow waters, but it can also grow in deeper lakes, provided the water is sufficiently clear to allow adequate light penetration (Preston & Croft 1997).

Part of the difficulty faced by anyone wishing to identify floating aquatic Utricularia species is collecting adequate specimens. Even in Europe, where there are only eight closely related native species, there remain unresolved taxonomic problems. Probably the most intractable problem for botanists working in B & I on these species is the fact that many populations persist overwinter and spread entirely vegetatively using leafy buds called 'turions' produced when growing conditions begin to falter or decline at the end of summer. The plants rarely or only intermittently flower in northern areas of B & I, yet the floral characters are vital requirements for correct identification (Preston & Croft 1997).

Flowering plants of U. vulgaris and U. australis are easily distinguished, but separation on vegetative characters is very difficult since the differences between the species are slight and they are too variable to enable ready identification. Identification of vegetative material with absolute certainty, which is often all that is present to work with, is really almost impossible or requires great expertise (Preston & Croft 1997).

Fermanagh occurrence

U. vulgaris s.l. is by far the most frequent and widespread of the four Utricularia forms found in Fermanagh, being more than twice as frequent as the next ranking U. minor (Lesser Bladderwort). The Fermanagh Flora Database contains records from 60 tetrads, 11.4% of the total in the VC and 59 of them have post-1975 records. While it is widespread in lowland lakes, the species is frequent only around Upper Lough Erne. U. vulgaris s.l. is very much a lowland species and it reaches its highest location in Fermanagh around Carricknagower Lough on the Western Plateau at an altitude of just 225 m.

U. vulgaris s.s. is reliably separable from U. australis (Bladderwort) only when in flower, and the current author (RSF) therefore believes that virtually all of the Fermanagh U. vulgaris records must be regarded as U. vulgaris s.l. which, however, occupies a wider range of habitats than U. vulgaris s.s., including acid bog pools. The only record of the 120 or so that exist of this aquatic that he believes might well be U. vulgaris s.s. is the find by Miss Nora Dawson (a very methodical and careful recorder) at Brockagh Point, Boa Island, Lower Lough Erne, made on 25 July 1976. Even in this case, unlike her record of U. australis, there is no mention of flowering.

Since flowers of these two Utricularia species are seldom found, and flowering is especially rare in cooler northern and western regions of B & I including Fermanagh, the true distribution of each segregate species of U. vulgaris s.l. is unknown and, indeed, it may be impossible to determine (Preston & Croft 1997).

Irish occurrence

The Cen Cat Fl Ir 2 indicates that U. vulgaris has been recorded in every VC, but the map published for U. vulgaris s.l. by Preston & Croft (1997) shows that it has not been found in several VCs in southern Ireland in the post-1950 period. The New Atlas map revises the situation somewhat, but there are still many hectads with pre-1970 records only. Now that the RSF and RHN have together concluded that the Fermanagh records should really lie within U. vulgaris s.l., the New Atlas map for U. vulgaris s.s. is unfortunately misleading.

In either sense, U. vulgaris appears to be declining, but as indicated, this may or may not be real since the two species are only expertly identified without flowers, and such identifications are not absolute. In any event, being submerged aquatics, both forms are easily overlooked and they remain under-recorded unless water bodies are actively dredged for specimens and vouchers kept. 

British occurrence

The New Atlas hectad map shows U. vulgaris s.l. thinly but widely scattered across Britain, with a greater representation of recent records in NW Scotland than appeared in the earlier BSBI Atlas (Perring & Walters 1962, 1976). The map also indicates a marked widespread decline of U. vulgaris s.l. across most parts of England (but especially the Midlands and South), Wales and E Scotland. Along with other aquatic species, there have undoubtedly been major population contractions due to habitat loss and change associated with drainage and intensification of agricultural practices, the species especially reacting adversely to excessive nutrient enrichment (George 1992; F.J. Rumsey, in: Preston et al. 2002).

European and world occurrence

Although knowledge of the true distribution is compromised by the confusion between U. vulgaris s.s. and U. australis already mentioned, U. vulgaris s.l. is believed to belong to the Eurosiberian temperate phytogeographical element (Preston & Hill 1997). U. vulgaris s.l. is widespread in Europe, both temperate and tropical Asia eastwards to Siberia and Tibet, and N Africa. It extends northwards to scattered localities in N Scandinavia, although it is absent from both Iceland and Greenland. It is rare in both the Mediterranean and towards its northern limit in Scandinavia (Sell & Murrrell 2009).

It also has a wide distribution elsewhere in the world, being introduced across Africa and to both Australia and New Zealand (Hultén & Fries 1986, Map 1720; Preston & Croft 1997; Sell & Murrell 2009).

Names

The genus name 'Utricularia' is derived from the Latin 'utriculus' meaning either 'a small bag', 'a small bladder', or 'a small bottle': in any event it refers to the minute bladder-like insect traps by means of which the plant supplements its nutrient supply (Gilbert-Carter 1964; Holmes 1979; Stearn 1992).

Threats

Drainage of shallow water bodies and excessive eutrophication are restricting available habitats.

References

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