Sunday, 27 August 2017

Sparganium erectum - Getting to Grips with the Subspecies

Mike Wilcox is taking an interest in Branched Bur-reed (Sparganium erectum) at the moment, with the aim of improving knowledge of the distribution of the four subspecies. Much needed, and particularly valuable for the New Atlas project.  It is too easy to ignore variation below the species level, but in recent years we have seen a number of under-recorded subspecies raised to species status leaving a black hole in our records as a result. Even where this is not warranted the ecology and geography of the component subspecies can diverge and is in itself interesting.

                                   Sparganium erectum subsp. microcarpum on the Ripon Canal. Image: M. Wilcox

So ideally we should be recording subspecies, although it is not always easy especially when published descriptions are often inadequate. It is too easy to make a false start, reducing confidence and increasing the inclination not to try. Which neatly brings me back to Mike, who is keen to receive samples of mature fruiting heads from anywhere in the UK and Ireland and will provide or confirm the initial ID's. So its win win for all concerned.

There are four subspecies in the UK & Ireland, all of which are detailed in our standard floras. So they are doable, but only with mature fruit (so now onwards is a great time to collect fruit) and being aware of the pitfalls in the key. The split between subsp. microcarpum and subsp. neglectum is particularly tricky as it relies on a judgement as to whether the individual fruit are 'shouldered' or 'gradually narrowed'. See Mike's photo of the former and note the difference between the mature fruit and the immature fruit. Subsp. microcarpum might perhaps be better described as having a domed head as it is not markedly shouldered, and subsp. neglectum as tapering. There is a great picture of the latter (and subsp. erectum) here.

If you would like to get in touch with Mike his address is in the BSBI members handbook (Members area of the website) or drop him an email. Fruiting heads can be put into a paper packet or envelope, and full details of the location should be provided (there is no value in a record if we don't know where it comes from!). You can email Mike at michaelpw22[at]  (replace the [at] with an @).

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