Callitriche obtusangula Le Gall, Blunt-fruited Water-starwort

Account Summary

Fermanagh occurrence

There are just six Fermanagh sites for this apparently rare perennial Water-starwort recorded in five tetrads as the accompanying map shows, three around Upper Lough Erne and two in isolated lakelets on the eastern boundary of the VC. Only one of the seven records has a voucher in BEL and, rather surprisingly, C. obtusangula was not observed at all in the VC by the very thorough and extensive NI Lakes Survey carried out between 1988 and 1991.

Locally, it is very rarely recorded in still or slow-moving water in lowland lakes, streams and ditches. The details of the other Fermanagh records are: N shore of Moorlough Lake, 1946-53, MCM & D; wet ditch, Inishroosk, Upper Lough Erne, June 1974, P. Hackney, voucher in BEL; Rabbit Island, Upper Lough Erne, 5 August 1986, S.J. Leach & A.S. McMullin; Colebrooke River estuary, Kilmore Td, Upper Lough Erne, S.J. Leach & A.S. McMullin (two sample areas recorded); and Rose Lough, Mullycanvan Td, 20 July 1988, RHN & J.S. Faulkner.

Habitat preferences

As with all Callitriche spp., the species is taxonomically difficult and C. obtusangula occurs in still to slow-flowing, mesotrophic and eutrophic water, perhaps most abundantly over calcareous soils, but also over peaty substrata. It is strictly a lowland species. In coastal areas, it can grow in brackish water, typically in ditches in grazing marshes. Terrestrial forms grow on damp mud at the water's edge and are always annuals (Preston & Croft 1997).

The aquatic form of C. obtusangula is a perennial with a life-form similar to C. platycarpa (Various-leaved Water-starwort) and the two species frequently occur together – plants overwintering as submerged shoots with linear leaves. In the spring and summer, the stems grow to reach the water surface where they develop floating rosettes. Plants in still or quieter, slow-flowing waters can develop large, dense beds under favourable conditions and flower and fruit freely, while those in faster-flowing conditions generally remain submerged and may fail to fruit (David 1958; Lansdown 2008).

British and Irish occurrence

C. obtusangula is widespread in England and

Wales south of a line between Lancaster and Hull, but it quickly becomes rare and widely scattered northwards and it is very rare or absent in most of Scotland. In Ireland, it is scattered down both the W & E coasts, and apart from a few hectads along the River Shannon, decidedly rare or absent in the centre of the island.

Preston & Croft (1997) stated that in their opinion, while C. obtusangula is a fairly distinctive species, it is almost certainly under-recorded in B & I, being most likely confused with C. stagnalis (Common Water-starwort). However, with so few records here in Fermanagh and, indeed, similarly elsewhere in most of B & I, more careful, systematic recording is required to determine the true picture of its occurrence and distribution.

European occurrence

C. obtusangula belongs to the suboceanic southern-temperate phytogeographical element and, on the continental mainland, it occurs from the Netherlands to Austria and the former Yugoslavia in the east, and from there, westwards along the Mediterranean coast, including on the islands of Corsica and Sardinia, into Spain and Portugal. It also occurs in N Africa, in both Morocco and Tunisia (Lansdown 2008; Sell & Murrell 2009).

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