BSBI Plant Referee on the case, Part II

Giant Horsetail - in close-up
Image: M. Allen

Last month, we reported on what happened when Martin found an unusual Horsetail and, as a BSBI member, was able to contact the BSBI's expert referee for Horsetails. Now here's the second part of Martin's story: 

"Thanks to Pat, the BSBI’s expert referee, I now know that what I found was an unusual form of Giant Horsetail. 

When Pat searched the shelves of the Natural History Museum Herbarium (which has one of the most important collections of ferns and other seed-free vascular plants in the world) there was not one there with secondary branching. 

Giant Horsetail - in abundance!
Image: M. Allen

However, recently Pat found one in the field with “most stems having a solitary secondary branch per stem somewhere near around two thirds up and it was on many of the stems” and so had to change his notes from ‘never’ to ‘rarely branches’. 

Pat then told me: “Early this year or last I was sent a specimen that had enormous numbers of secondary branches but right along the branches unlike your ones which seemed to be concentrated around the middle close to the stem … Therefore, I have only seen three in recent years with this condition but it may just be that I never looked before. I always do now.” 

Close-up showing secondary
branching on Field Horsetail
Image: M. Allen 

So, I’m very pleased to have been able to add to the sum of knowledge about our UK flora – hopefully the UK Floras we use in the field will be updated in time with a change of ‘never’ to ‘rarely’ – though I’m still rather bewildered that I never noticed it before in over ten years of visiting that wood, which considering the vast patches that are present next to the path seems to be quite a tricky feat!

Following on from this I started to notice secondary branching in another Horsetail I saw whilst out surveying. I sent a couple of specimens to Pat because I thought they were Field Horsetail (Equisetum arvense), but again was confused as my field Flora says it is only simply branched. 

Pat writes “I regularly find secondary branching on larger plants of E. arvense with green stems but also a lot on the larger stemmed plants where the internodes are turning or are mostly white.” And that “this is a reasonably common affair in large colonies of E. arvense.”

Secondary branching 
on Field Horsetail 
Image: M. Allen 

It seems to be reasonably common near me too as I noted at least eight different sites locally over the last few months – it made me wonder how many of us note the secondary branching and assume it is Wood Horsetail (often given as the only UK Horsetail with secondary branching): A useful reminder to look closely at other features too before making an identification".

Many thanks to Martin for these useful notes about Horsetails and a timely reminder of how incredibly helpful and approachable BSBI's expert plant referees are! I hope Martin's comments encourage fellow members, whatever their skill level, to use the referee service more frequently.