Utricularia stygia G. Thor., Nordic Bladderwort

Native, very rare, but probably overlooked and under-recorded.

8 August 2006; ENSIS Lake Survey Team; Lough Wee.

As mentioned under the previous taxon, U. intermedia s.l., this is a poorly recorded submerged aquatic species of cool, wet, acid pools and lakes, where the presence of plants is often masked by opaque brown peaty water. Following some pioneering taxonomic work on this genus in Scandinavia during the late 1980s (Thor 1987, 1988), the determination of this taxon requires careful microscopic examination of amongst other characters, the angles between branched quadrifid hairs lining the walls of the bladder traps (T.C.G. Rich, in: BSBI Plant Crib 1998). This microscopic examination is a specialised skill and, to avoid distortion of the crucial angles between the hairs on the bladder lining, it ideally requires fresh un-pressed voucher specimens. Consequently, and unsurprisingly, relatively few botanists in B & I have yet obtained sufficient experience in order to determine correct identifications.

A fresh survey of selected lakes in NI, commissioned by NIEA and carried out by English botanists in summer 2006, found Utricularia specimens in two Fermanagh lakes that subsequently were determined as U. stygia by the specialist, N.F. Stewart. In personal correspondence with RSF in November 2010, Stewart affirmed that he had examined the quadrifid hairs of Fermanagh specimens he had received, and he stated that over 99% of all the U. intermedia agg. specimens he had examined from across B & I, had turned out to be U. stygia.

The details of the second lake where this species was collected are: Tullymore Lough, 12 August 2006, ENSIS Lake Survey Team. The Flora of Co Tyrone includes mention of a 1999 record there of U. stygia from Innaghachola Lough, det P. Hackney and J.J. Day. Further to the above, a published study of Irish herbarium specimens carried out in Dublin found considerable difficulty separating U. stygia from U. ochroleuca s.s. (Doyle & Parnell 2003).