Bur-reeds

Back in 2008 I sent some seed heads of Sparganium angustifolium (Floating Bur-reed) from Raasay to Kay Fuhrmann at the Lower Saxony State Museum Oldenburg. She has just published a paper on S. angustifolium and S. emersum (Unbranched Bur-reed) in Northwest Germany, the Netherlands and Belgium and says that many of the 67 populations studied “share characters which are intermediate between the traits of Sparganium angustifolium and the closely related S. emersum. Although two hypotheses exist, one assumes two hybridizing species; the other emphasizing a single variable taxon, the real relationship seems still not to be understood.” She says that molecular studies are on their way and first results will hopefully follow soon.

This is interesting in the local context because there are quite a few records for S. emersum in the vice-county but neither I nor my predecessor who was VCR for 40 years have ever seen it here. One of the records refers to a population on Raasay that certainly stretches  the leaf-width characteristic of S. angustifolium to the limit, but in 2005 I sent a specimen to the BSBI referee, Prof Christopher D. K. Cook in Switzerland who said “I can find no reason for it not being Sparganium angustifolium“.

Interestingly, a  1954 record of S. emersum from Fladday (off Raasay) is down to him and also in a 1961 paper on Sparganium in Britain in Watsonia he said: “Many hybrids have been reported, but the only hybrids I have seen (including examination of herbarium material) are between S. emersum and S. angustifolium. These two species are fairly widely separated ecologically, the former being a species of eutrophic and the latter a species of oligotrophic waters, but they occasionally grow close together in parts of western Scotland. The hybrids appear to be fully fertile and many plants have been found that showed introgression. At Stoer in Sutherland and on the Isle of Raasay the appearance of the hybrids tends towards S. emersum while in Galloway introgression appears to be towards S. angustifolium.”  I quizzed him about this back in March and he said “I have feeling that the hybrids were from pools behind the beach at Brochel. Real evidence should be in the Edinburgh herbarium.”  Sadly, no such specimens have been located at RBGE.

All very fascinating. I await further results from Kay with interest.

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