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On Dandelion but the measurements seem too small for either Puccinia variabilis or Puccinia hieracii ….. Aeciaspores (?) 17-24 x 17-22 µm, teliospores 1-septate 24-30 x 17-18 µm.
[attachment=2]w Tarax 150526 154b taraxacum.jpg[/attachment] 
[attachment=1]w Tarax1 150526-2 17-24.jpg[/attachment] 
[attachment=0]w Tarax2 150526-1 24-30×17-18.jpg[/attachment] Hi Jenny I think this will prove to be
P. variabilis– I think I can make out the pores on the uredospores. A useful trick is to mount in cotton blue in lactophenol, pop a cover slip on and heat the slide until it juststarts to bubble, You will find that this procedure clears the spores somewhat, makes the pores much more obvious (therefore easier to count), and – extremely helpfully – preferentially stains the spore wall at the former point of attachment, thus making it even easier to mentally orientate the spores to work out whether the pores are equatorial or supra-equatorial. best wishes
Chris
* I know I split an infinitive – but it’s getting late
😳 Thank you Chris – I’m struggling to tell the difference between aeciaspores and uredospores though … 😳 How best should I heat the slide – over a lighter flame or something a bit more refined?!
Sorry Jenny I had missed this – yes a lighter would be fine. Don’t worry, telling aeciospores from uredospores can be confusing at times, but in the majority of cases the shape of the sorus is a clue – most
Pucciniaand Uromyces(i.e. the majority of British rusts) have aecia as cluster-cups, so it’s straightforward. Based on host, reading through Wilson & Henderson should enable you to work out what you’re looking at. best
Chris
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